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New interface design for MythTV
MythTV 0.22 will be sporting a new interface design. Features include animation, better interactivity, and faster and easier development for themers and developers...
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Zap2It Labs discontinuing free TV guide service
Zap2It Labs have announced (cache) via their webpage that, due to abuse of the service, data will no longer be available after September 1st. There is no other direct source, and no option to pay for the service even if the users wanted to...
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UK petition for free TV listings
http://petitions.pm.gov.uk/Free-TV-listings/ being run to make all UK television listings freely available under royalty-free terms such as a Creative Commons License....
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New server
DreamHosts.

I have had to drop the mirrors, atleast temporarily, as the new site is bandwidth limited.
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Sky Anytime for Any PC?
Advogato has pointed out (cache) that Sky's advertising of their new Anytime package doesn't actually run on *any* PC. It requires Windows.

lkcl suggests the advertising is in breach of the ASA guidelines and goes on to point out the many devices runing GNU/Linux Sky is now utilising, including the set-top box, and the modified/pre-configured Netgear DG834GT for the broadband service.

Under the GPL license, Sky should provide the source code free of charge...
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Interview with pcHDTV Founder/CEO
Open Addict has an interview (cache) with Jack Kelliher, Founder and CEO of pcHDTV, the Linux-focused hardware company that markets HDTV cards.

Their flagship product is the HD-5500 (cache) HDTV PCI card which supports the popular MythTV Linux PVR application...
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New HDTV chips announced at Consumer Electronics Show
CES show has seen the launch of a raft of new HDTV chips.

Conexant has added two video decoders for HDTV personal video recording (PVR) set-top boxes. The CX2427X is a dual-channel video decoder that can decode two HDTV programmes simultaneously, and supporting PVR applications on up to two televisions, eliminating the need for a dedicated STB receiver for each TV.

For the cable market, Broadcom has developed an HDTV Chip with a programmable security engine that has the hardware included to support all the current conditional access systems. This will avoid the need for subscriber cards, which are costly to distribute and vulnerable to hackers, and allow new CA algorithms to be downloaded to the cableboxes...
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Sky+ tops 2 million mark

The rapid growth of Sky+ highlights increasing demand from customers for the ability to take control over their television viewing. With 2 million active boxes, almost 5 million viewers are using Sky+ to record without video tape, pause and rewind live TV, and record all episodes of a favourite series at the touch of a button...
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KWorld introduces dual hybrid TV tuner
KWorld has announced a new TV tuner in the form of the DVB-T PE310 (cache). The DVB-T PE310 is a dual hybrid TV tuner PCI-Express card initially designed for the UK market.
The DVB-T PE310 sports two tuners, both of which are capable of displaying analog and digital signals, which means that you can tune into two analog sources, or two digital sources or even one analog and one digital at the same time.
On top of that, you can use the additional AV/S-Video input for CVBS, S-video or SPDIF connections...
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MythTV developer on ExtremeTech
MythTV, has an article on ExtremeTech (cache) about his book Hacking MythTV (cache). In this article, he reviews the 'Top Plugins for MythTV' ...
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Quitting Smoking Through Hypnosis
By Abbey Grace Yap

Article Directory: http://www.articlecube.com

The writer, Abbey Grace Yap, is an active advocate for health consciousness and disease awareness. She possesses a deep passion in discovering new health-related information and sharing it to her readers.DrugstoreTM.com is a reputable online drug store. From sexual health to a woman's health, sleeping aids to weight loss pills, our online pharmacy offers convenient customer access to various health medicines, including an array of health product and medicare prescription drug.www.drugstoretm.com/soma.php">Buy Soma | Buy Tramadol

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Lisp in Ruby
<p style="padding-left:3em;"><em>I stumbled across <a href="http://bc.tech.coop/blog/080101.html">this</a> and it got me thinking &#8230;</em></p> <h3>Update</h3> <p style="padding-left:3em;"><em>I&#8217;ve updated the Textile formatter on the site and the code for this entry is now displaying correctly. The previous version was swalling the == operators in the code.</em></p> <h2>Lisp 1.5 Programmer&#8217;s Manual</h2> <p>I stumbled across <a href="http://bc.tech.coop/blog/080101.html">this</a> in Bill Clementson&#8217;s blog and remembered using the Lisp 1.5 Prgrammers manual from the college years. I have strong memories of pouring over that particular page in the manual and attempting to understand all the nuances.</p> <p>If you&#8217;ve never read the Lisp 1.5 Programamers Manual, page 13 is the guts of a Lisp Interpreter, the &#8220;eval&#8221; and &#8220;apply&#8221; functions. It is written in Lisp, although the notation used is a bit funky. The entire interpreter (minus two utility functions) is presented on a single page of the book. Talk about a concise language definition!</p> <h2>In Ruby?</h2> <p>I had often thought about implementing a Lisp interpreter, but back in the &#8220;old days&#8221;, the thought of implementing garbage collection and the whole runtime thing was a bit daunting. This was in the day before C, so my implementation language would have been assembler &#8230; yech.</p> <p>But as I was reviewing the page, I realized that with today&#8217;s modern languages, I could problably just convert the funky M-Expressions used on page 13 directly into code. So &#8230; why not?</p> <h2>The Code</h2> <p>Here is the complete Ruby source code for the Lisp interpreter from page 13 of the Lisp Programmers manual:</p> <pre> # Kernel Extensions to support Lisp class Object def lisp_string to_s end end class NilClass def lisp_string "nil" end end class Array # Convert an Array into an S-expression (i.e. linked list). # Subarrays are converted as well. def sexp result = nil reverse.each do |item| item = item.sexp if item.respond_to?(:sexp) result = cons(item, result) end result end end # The Basic Lisp Cons cell data structures. Cons cells consist of a # head and a tail. class Cons attr_reader :head, :tail def initialize(head, tail) @head, @tail = head, tail end def ==(other) return false unless other.class == Cons return true if self.object_id == other.object_id return car(self) == car(other) &#38;&#38; cdr(self) == cdr(other) end # Convert the lisp expression to a string. def lisp_string e = self result = "(" while e if e.class != Cons result &lt;&lt; ". " &lt;&lt; e.lisp_string e = nil else result &lt;&lt; car(e).lisp_string e = cdr(e) result &lt;&lt; " " if e end end result &lt;&lt; ")" result end end # Lisp Primitive Functions. # It is an atom if it is not a cons cell. def atom?(a) a.class != Cons end # Get the head of a list. def car(e) e.head end # Get the tail of a list. def cdr(e) e.tail end # Construct a new list from a head and a tail. def cons(h,t) Cons.new(h,t) end # Here is the guts of the Lisp interpreter. Apply and eval work # together to interpret the S-expression. These definitions are taken # directly from page 13 of the Lisp 1.5 Programmer's Manual. def apply(fn, x, a) if atom?(fn) case fn when :car then caar(x) when :cdr then cdar(x) when :cons then cons(car(x), cadr(x)) when :atom then atom?(car(x)) when :eq then car(x) == cadr(x) else apply(eval(fn,a), x, a) end elsif car(fn) == :lambda eval(caddr(fn), pairlis(cadr(fn), x, a)) elsif car(fn) == :label apply(caddr(fn), x, cons(cons(cadr(fn), caddr(fn)), a)) end end def eval(e,a) if atom?(e) cdr(assoc(e,a)) elsif atom?(car(e)) if car(e) == :quote cadr(e) elsif car(e) == :cond evcon(cdr(e),a) else apply(car(e), evlis(cdr(e), a), a) end else apply(car(e), evlis(cdr(e), a), a) end end # And now some utility functions used by apply and eval. These are # also given in the Lisp 1.5 Programmer's Manual. def evcon(c,a) if eval(caar(c), a) eval(cadar(c), a) else evcon(cdr(c), a) end end def evlis(m, a) if m.nil? nil else cons(eval(car(m),a), evlis(cdr(m), a)) end end def assoc(a, e) if e.nil? fail "#{a.inspect} not bound" elsif a == caar(e) car(e) else assoc(a, cdr(e)) end end def pairlis(vars, vals, a) while vars &#38;&#38; vals a = cons(cons(car(vars), car(vals)), a) vars = cdr(vars) vals = cdr(vals) end a end # Handy lisp utility functions built on car and cdr. def caar(e) car(car(e)) end def cadr(e) car(cdr(e)) end def caddr(e) car(cdr(cdr(e))) end def cdar(e) cdr(car(e)) end def cadar(e) car(cdr(car(e))) end </pre> <h2>An Example</h2> <p>And to prove it, here&#8217;s an example program using Lisp. I didn&#8217;t bother to write a Lisp parser, so I need to express the lists in standard Ruby Array notation (which is converted to a linked list via the &#8220;sexp&#8221; method).</p> <p>Here&#8217;s the ruby program using the lisp interpreter. The Lisp system is very primitive. The only way to define the function needed is to put them in the environment structure, which is simply an association list of keys and values.</p> <pre> require 'lisp' # Create an environment where the reverse, rev_shift and null # functions are bound to an appropriate identifier. env = [ cons(:rev_shift, [:lambda, [:list, :result], [:cond, [[:null, :list], :result], [:t, [:rev_shift, [:cdr, :list], [:cons, [:car, :list], :result]]]]].sexp), cons(:reverse, [:lambda, [:list], [:rev_shift, :list, nil]].sexp), cons(:null, [:lambda, [:e], [:eq, :e, nil]].sexp), cons(:t, true), cons(nil, nil) ].sexp # Evaluate an S-Expression and print the result exp = [:reverse, [:quote, [:a, :b, :c, :d, :e]]].sexp puts "EVAL: #{exp.lisp_string}" puts " =&gt; #{eval(exp,env).lisp_string}" </pre> <p>The program will print:</p> <pre><code>$ ruby reverse.rb EVAL: (reverse (quote (a b c d e))) =&gt; (e d c b a)</code></pre> <p>All I need to do is write a Lisp parser and a <span class="caps">REPL</span>, and I&#8217;m in business!</p> <h2>The Example in Standard Lisp Notation</h2> <p>If you found the Ruby-ized Lisp code hard to read, here is the reverse funtions written in a more Lisp-like manner.</p> <pre> (defun reverse (list) (rev-shift list nil)) (defun rev-shift (list result) (cond ((null list) result) (t (rev-shift (cdr list) (cons (car list) result))) )) </pre>
The Arc Challenge
<p style="padding-left:3em;"><em>Paul Graham issues the Arc Challenge &#8230; who could resist?</em></p> <h2>Paul Graham&#8217;s Arc Challenge</h2> <p>You can read about the Arc Challenge here: <a href="http://www.paulgraham.com/arcchallenge.html">The Arc Challenge</a>. Go ahead a read it now, but I will summarize the challenge.</p> <p><strong>Write a web program such that:</strong></p> <ul> <li>The first page of the program displays nothing but a text box and a submit button. You enter some arbitrary text and press the submit button, which takes you to &#8230;</li> </ul> <ul> <li>The second page is nothing but a single link labeled &#8220;click here&#8221;. The <span class="caps">URL</span> linked to must not contain the text entered in the first step (i.e. you are not supposed to pass the text as a parameter on the link). Clicking the link takes you to &#8230;</li> </ul> <ul> <li>The third page which contains &#8220;You said: <span class="caps">XXX</span>&#8221; (where <span class="caps">XXX</span> is the text you entered in the first step).</li> </ul> <p>Here&#8217;s a screen cast demoing my solution to the Arc Challenge. (We will show the code shortly).</p> <object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" width="466" height="281"> <param name="movie" value="http://content.screencast.com/bootstrap.swf"></param> <param name="quality" value="high"></param> <param name="bgcolor" value="#FFFFFF"></param> <param name="flashVars" value="thumb=http://content.screencast.com/media/762eebca-fa50-49f8-9b88-dc7652bd3c9a_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_Thumbnail.gif&#38;content=http://content.screencast.com/media/499ec89e-b124-4dcb-bcd0-e74f6fac495f_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_00000084.swf&#38;width=466&#38;height=281"></param> <param name="allowFullScreen" value="true"></param> <param name="scale" value="showall"></param> <param name="allowScriptAccess" value="always"></param> <embed src="http://content.screencast.com/bootstrap.swf" quality="high" bgcolor="#FFFFFF" width="466" height="281" type="application/x-shockwave-flash" allowScriptAccess="always" flashVars="thumb=http://content.screencast.com/media/762eebca-fa50-49f8-9b88-dc7652bd3c9a_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_Thumbnail.gif&#38;content=http://content.screencast.com/media/499ec89e-b124-4dcb-bcd0-e74f6fac495f_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_00000084.swf&#38;width=466&#38;height=281" allowFullScreen="true" scale="showall"></embed> </object> <h2>Paul&#8217;s Solution</h2> <p>Paul has been working on designing Arc, his ideal programming language for the future. Given Paul&#8217;s language preferences, it is no surprise that Arc is very Lisp-like. Here is Paul&#8217;s solution written in Arc:</p> <pre class="testcode"> (defop said req (aform [w/link (pr "you said: " (arg _ "foo")) (pr "click here")] (input "foo") (submit))) </pre> <p>Paul points out that the solution is very short and elegant, only 23 nodes in the codetree. I&#8217;m sure I don&#8217;t quite understand exactly what it is doing (I&#8217;d love to see a step by step explanation of the code). He wonders what it would look like in other languages.</p> <p>Several people have responded with solutions in their own languages. I&#8217;ve seen a <a href="http://www.lukas-renggli.ch/blog/take-the-arc-challenge?_s=BXjPNOJFnBmoYxtA&#38;_k=lERhwwWC">Smalltalk Solution</a> as well as a <a href="http://arc-challenge.heroku.com/">Ruby solution</a> (which pretty closely mimics the Arc code from Paul) on the <a href="http://arclanguage.org/item?id=722">Arc Language Forum</a> page that was setup for responses.</p> <h2>Continuation Web Servers</h2> <p>The Arc challenge is a perfect candidate for a continuation based server solution. And I recalled that Chad Fowler and I had written a demo continuation based server for the <a href="http://onestepback.org/articles/callcc/">Continuations Demystified</a> talk we did at RubyConf 2005. (Look for the &#8220;Poor Man&#8217;s Seaside Demo in that presentation.) I wondered how easy it be to code up an Arc challenge solution using that code base.</p> <p>The key to a continuation based server is that it allows the programmer to code in a linear fashion. All the request/response nature of web interaction is completely hidden from you as a programmer.</p> <p>For example, let&#8217;s pretend we wanted to solve the Arc challenge using a terminal and command line rather than a web based solution. How would you write it? Probably something like this:</p> <pre class="rubycode"> text = gets puts "click here" gets puts "You said: #{text}" </pre> <p>Simple, linear programming. (OK, printing &#8220;click here&#8221; is silly in a text program, but you get the idea). You ask a question and read a response. You pause for a click. You then tell the user what the result is.</p> <p>Ask. Pause. Tell.</p> <p>Those are our basic abstract operations for this problem. Lets rewrite our text based solution using these abstractions. We&#8217;ll put this in a file called &#8220;arc_challenge.rb&#8221;.</p> <pre class="rubycode"> Conversation.interact do |io| text = io.ask io.pause("click here") io.tell("You said: #{text}") end </pre> <p>I&#8217;ve introduced three operations (methods) that are provided by an I/O object (let&#8217;s ignore the interact line for now). &#8220;ask&#8221; will ask the user for input, returning the string. &#8220;pause&#8221; will pause until the user indicates he/she is ready to continue (e.g. pressing return in our command line version). &#8220;tell&#8221; sends the given string to the user.</p> <p>So, what does &#8220;Conversation.interact&#8221; do? It creates the environment where the user have a conversation with the program. The interation is controlled through our ask/pause/tell functions provided by the I/O object passed to the interact block.</p> <p>Here is an implementation of a text based conversation.</p> <pre class="rubycode"> class TextBased def interact yield(self) end def ask(prompt=nil) print prompt, " " if prompt gets.chomp end def pause(prompt="") print prompt, " " if prompt gets end def tell(message) puts message end end Conversation = TextBased.new </pre> <p>To run the text based conversation, just require the text. Here&#8217;s a demo:</p> <object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" width="465" height="238"> <param name="movie" value="http://content.screencast.com/bootstrap.swf"></param> <param name="quality" value="high"></param> <param name="bgcolor" value="#FFFFFF"></param> <param name="flashVars" value="thumb=http://content.screencast.com/media/1ae5f9ce-5bc5-4360-8cbc-83b165a434ab_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_Thumbnail.gif&#38;content=http://content.screencast.com/media/90dd373a-0352-4710-acb1-6b18620a5609_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_00000080.swf&#38;width=465&#38;height=238"></param> <param name="allowFullScreen" value="true"></param> <param name="scale" value="showall"></param> <param name="allowScriptAccess" value="always"></param> <embed src="http://content.screencast.com/bootstrap.swf" quality="high" bgcolor="#FFFFFF" width="465" height="238" type="application/x-shockwave-flash" allowScriptAccess="always" flashVars="thumb=http://content.screencast.com/media/1ae5f9ce-5bc5-4360-8cbc-83b165a434ab_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_Thumbnail.gif&#38;content=http://content.screencast.com/media/90dd373a-0352-4710-acb1-6b18620a5609_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_00000080.swf&#38;width=465&#38;height=238" allowFullScreen="true" scale="showall"></embed> </object> <h2>Arc on the Web</h2> <p>Well, anybody can solve the challenge in text mode. How much work do we have to do to get it on the web.</p> <p>The answer: Zero!</p> <p>The code Chad and I wrote for <a href="http://onestepback.org/articles/callcc/">Continuations Demystified</a> includes a web-based version of the conversation object that is ready to go. All we have to do is plug it in and run it. No changes are required to our basic Arc challenge solution.</p> <p>Again, a screen demo:</p> <object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" width="538" height="352"> <param name="movie" value="http://content.screencast.com/bootstrap.swf"></param> <param name="quality" value="high"></param> <param name="bgcolor" value="#FFFFFF"></param> <param name="flashVars" value="thumb=http://content.screencast.com/media/a8773d13-5fe0-46f2-adcf-8ae4830c6e53_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_Thumbnail.gif&#38;content=http://content.screencast.com/media/2918dffc-1f80-401b-8063-d8c8bb908016_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_00000082.swf&#38;width=538&#38;height=352"></param> <param name="allowFullScreen" value="true"></param> <param name="scale" value="showall"></param> <param name="allowScriptAccess" value="always"></param> <embed src="http://content.screencast.com/bootstrap.swf" quality="high" bgcolor="#FFFFFF" width="538" height="352" type="application/x-shockwave-flash" allowScriptAccess="always" flashVars="thumb=http://content.screencast.com/media/a8773d13-5fe0-46f2-adcf-8ae4830c6e53_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_Thumbnail.gif&#38;content=http://content.screencast.com/media/2918dffc-1f80-401b-8063-d8c8bb908016_e67edb68-7ed6-4b26-9b5e-cd2fd2207a40_static_0_0_00000082.swf&#38;width=538&#38;height=352" allowFullScreen="true" scale="showall"></embed> </object> <p>Yes, we know that although we now have our Arc Challenge on the web, we haven&#8217;t quite conformed to the exact requirements of the challenge. We will handle that next.</p> <h2>The Final Arc Solution</h2> <p>The problem is that the current Web based conversation object makes all kinds of assumptions that are not appropriate for the final Arc solution.</p> <p>In particular, we need to change:</p> <ul> <li>Get rid the head line, restart link and other extraneous <span class="caps">HTML</span> elements.</li> </ul> <ul> <li>Don&#8217;t keep a running log of the conversation. When you move to a new page, you start from scratch.</li> </ul> <ul> <li>The &#8220;click here&#8221; should be a real link, not just a text box where you can press enter.</li> </ul> <p>To get to here, we will have to make some modifications to the conversation web library. It turns out the changes are pretty straight forward. The whole interaction framework is controlled by the Conversation object that implements ask/pause/tell methods. You can see the changes made for the Arc challenge in the &#8220;noecho_web_based.rb&#8221; file (see the end of this post for the availability of the source code).</p> <h2>The Final Conversation Based Solution</h2> <p>In cased you missed it, here is the Arc Challenge Solution:</p> <pre class="rubycode"> Conversation.interact do |io| text = io.ask io.pause("click here") io.tell("You said: #{text}") end </pre> <p>Yep, it&#8217;s the exact same file we used for the text based solution. I don&#8217;t know if it is as elegant as Paul&#8217;s version, but I certainly find it easy to read and understand. (Rerun the <a href="http://www.screencast.com/t/mFoZAA7N">very first screen cast</a> in this posting if you want to see it in action again).</p> <p>If you want to look at the code, there is a <a href="http://onestepback.org/download/conversations.tgz">tarball</a> available that contains all the continuation server demo code from <a href="http://onestepback.org/articles/callcc/">Continuations Demystified</a> talk, as well as the two new files I added for the Arc challenge. &#8220;arc_challenge.rb&#8221; is the actually solution and &#8220;noecho_web_based.rb&#8221; is the conversation library that renders the solution in the style set forth by the challenge.</p> <p>Enjoy.</p>
Erlang-like Method Definition in FlexMock
<p style="padding-left:3em;"><em>Some fun with Erlang and FlexMock.</em></p> <h2>Erlang Function Definitions</h2> <p>Erlang defines functions by listing a set of possible argument lists and the body of the function to be executed for each argument list. For example, the factorial function might be defined in Erlang as:</p> <pre> factorial(0) -&gt; 1; factorial(N) -&gt; N * fac(N-1). </pre> <p>If factorial is called with a 0 (zero) for an argument, the first argument list will be chosen and the value of the factorial function will be 1. Otherwise, the value returned will be calculated by a recursive call to factorial.</p> <h2>FlexMock and Erlang</h2> <p>While playing around with FlexMock the other day, I realized that it does parameter matching, much like Erlang, when deciding what mock method to call. So I started wondering if you could write Erlang-like function definitions in FlexMock.</p> <p>Here&#8217;s the result.</p> <pre> mock = flexmock('fact') mock.should_receive(:factorial).with(0).and_return(1) mock.should_receive(:factorial).with(Integer). and_return { |n| n * mock.factorial(n-1) } </pre> <p>Ok, that was fun. But let&#8217;s not start building entire systems using nothing but FlexMock.</p>
FlexMock 0.6.4 Release
<p style="padding-left:3em;"><em>New Release of FlexMock</em></p> <h2>FlexMock 0.6.4 Release</h2> <p>Just wanted to drop a quick note that a new version of FlexMock is now available.</p> <p>There are two nice enhancements and a minor bug fix in this version.</p> The first enhancement is for mocking ActiveRecord objects. The folks at EdgeCase use a mockmodel() method for the RSpec mock that returns a mock that has some common ActiveRecord methods mocked (stubbed) with some reasonable values. This make is a bit more convenient when mocking Rails models. FlexMock now supports this natively, just say <code>flexmock(:model, YourRailsModel)</code> to create a mock object that mimics a YourRailsModel object. <p>The second enhancement is in regard to the <a href="http://onestepback.org/index.cgi/Tech/Ruby/FlexMockReturns.red">What Should flexmock(real_obj) Return?</a> question I blogged about last May. I asked the question: What should flexmock(real_obj) return, the real object or the mock object? Someone had suggested returning the real object when flexmock() is given a block. There was some positive response to that, so that was included in the FlexMock release.</p> <p>But after several months of using it, I found it difficult to remember which version of flexmock() returned what. At one point I found myself caling flexmock() with an empty block, just to get the real object back. That was madness.</p> <p>So starting with release 0.6.4, flexmock will always return the real object. This is the best of both worlds, but it comes with a small price. Real objects partially mocked by FlexMode will now be enhanced with some extra methods, just enough methods so that addition mock behavior can be added to it. For example, <code>should_receive</code> is added to the partially mocked real object. This pollutes the method namespace for an object, but the result is much simplier for the programmer to use. If you <strong>really</strong> want to avoid method namespace pollution, there is a :safe mode offered. Read the docs for all the gory details.</p> <h2>By The Way, If You Grabbed Version 0.6.3 &#8230;</h2> <p>If you are one of the handful of people that downloaded verion 0.6.3 yesterday, then go ahead and grab 0.6.4. The only difference is in the <span class="caps">API</span> for mocking ActiveRecord models. After using it for a bit, I realized that the <span class="caps">API</span> could be improved, hence version 0.6.4. Sorry about that.</p>
Using FlexMock to Test Computational Fluid Dynamics Code
<p style="padding-left:3em;"><em>This is a fun example of using FlexMock</em></p> <h2>Andrew Sweeney Asks:</h2> <p>Andrew Sweeney emailed me with the following question:</p> <p style="padding-left:3em;"><em>I am currently working on a ruby project in which I think flexmock would be a good fit for unit testing. I have read the documentation and gone over the examples however fail to wrap my head around how to apply flexmock to my own app. I was hoping that you could give me some guidence and get me started or point me in the right direction. </em></p> <p>You can find his original source code <a href="http://wikis.onestepback.org/OSB/page/show/OriginalF3DQueueCode">here</a>.</p> <p>I thought his problem was interesting enough to write it up as an example of using FlexMock. Andrew and his mentor, <a href="http://www.workingwithrails.com/person/6007-bil-kleb">Bil Kleb</a> gave permission for me to reproduce the code in my blog. The F3DQueue class is part of a <a href="http://fun3d.larc.nasa.gov">Computational Fluid Dynamics</a> project (<a href="http://fun3d.larc.nasa.gov">http://fun3d.larc.nasa.gov</a>) at <span class="caps">NASA</span>.</p> <h2>Quick Code Review</h2> <p>The F3DQueue class is small, so there&#8217;s not a lot of code we need to wade through. We see it uses a second class named AutoF3D, but the only clues we have to what AutoF3D might do are the four method calls on the &#8220;job&#8221; object in the <ins>run</ins> method.</p> <p>It looks like the main interface to the queue object is the <ins>add_to_queue</ins> method. There is a thread started that pulls jobs (i.e. AutoF3D objects) from the queue and processes them in turn. There is some server delays built into the system. I presume that Computational Fluid Dynamics is, ummm, computationally complex and the delays are just there to make sure the workload does eat up <em>all</em> the <span class="caps">CPU</span> time on the server.</p> <h2>Starting Testing</h2> <p>When writing new code, I always like to approach it in a Test-First manner. Because I won&#8217;t write solution code without a test that forces me to write it, I have a high confidence that the code is well covered with tests.</p> <p>Unfortunately, dealing with legacy code means that the code is already written and the test-first approach won&#8217;t work. That&#8217;s ok, I have a little trick that I use. Just comment out the bodies of all the methods in the class you are about to test. Then write the tests that force you to <em>uncomment</em> the code. Just uncomment only enought to get the tests to pass, don&#8217;t uncomment anything you don&#8217;t have to. You have enough tests when all the code has been uncommented. The technique is <em>almost</em> as good as doing real test-first.</p> <h2>The Commented Out Version</h2> <p><a href="http://wikis.onestepback.org/OSB/page/show/CommentedF3DQueueCode">Here</a> is the code base as I started the test.</p> <h2>An Existence Test</h2> <p>I almost always start out with an existence test. Existence tests basically prove the proper files are included and the object can be created. Normally I delete these after a few tests have been written. But I left this one in for an example.</p> <pre class="testcode"> def test_initial_conditions q = F3DQueue.new assert_not_nil q end </pre> <p>Nothing really exciting here. Let&#8217;s move on &#8230;</p> <h2>Proving <span class="caps">FIFO</span> Queue Order</h2> <p>The first thing I want to prove is that items put into the queue are removed in <span class="caps">FIFO</span> order. Since <ins>add_to_queue</ins> creates a AutoF3D object, I mock out the <ins>new</ins> method on the class object and tell FlexMock to expect <ins>new</ins> to be called twice. Once with :a, :b, and :c as parameters, then again with :x, :y, :z paramters. Each invocation of <ins>new</ins> will return a different symbol (:first and :second) so we can easily test the items are pulled off the queue in <span class="caps">FIFO</span> order.</p> <p>Notice that I pass in simple symbols for the arguments to <ins>add_to_queue</ins>. Our code doesn&#8217;t interpret the values of the arguments, they are merely passed directly to the AutoF3D constructor. All we do is verify that the AutoF3D (mocked) constructor does indeed receive the arguments we pass in.</p> <p>Here&#8217;s the test:</p> <pre class="testcode"> def test_adding_to_queue_is_removed_in_fifo_order flexmock(AutoF3D).should_receive(:new).once.with(:a, :b, :c).and_return(:first).ordered flexmock(AutoF3D).should_receive(:new).once.with(:x, :y, :z).and_return(:second).ordered q = F3DQueue.new q.add_to_queue(:a, :b, :c) q.add_to_queue(:x, :y, :z) assert_equal :first, q.remove_from_queue assert_equal :second, q.remove_from_queue end </pre> <p>This test caused three changes. First, the <ins>add_to_queue</ins> method needed lines uncommented:</p> <pre class="rubycode"> def add_to_queue(modelLoc, params, gridFile) autoF3D = AutoF3D.new(modelLoc, params, gridFile) @queue.push autoF3D # $log.info 'Request added to queue' end </pre> <p>(Notice I didn&#8217;t uncomment the log. The logger is not needed to pass the test, and doesn&#8217;t contribute to the actual functionality of the method. I will not be testing the logger in the for the purposes of this article.)</p> <p>Also the <ins>remove_from_queue</ins> needed its body uncommented:</p> <pre class="rubycode"> def remove_from_queue @queue.pop end </pre> <p>And finally, the initializer code needed to create the queue array:</p> <pre class="rubycode"> def initialize @queue = [] # Thread.new{ process } end </pre> <p>Notice that the <ins>Thread.new</ins> line is left commented. We will deal with that in a bit.</p> <p>So now we run the test:</p> <pre class="shell"> $ ruby test_f3dqueue.rb Started F. Finished in 0.010184 seconds. 1) Failure: test_adding_to_queue_is_removed_in_fifo_order(TestF3DQueue) [test_f3dqueue.rb:23]: &lt;:first&gt; expected but was &lt;:second&gt;. 2 tests, 2 assertions, 1 failures, 0 errors </pre> <p>Oops! This test uncovered the first bug. The code as written has stack behavior (i.e. <span class="caps">LIFO</span>). The naming seems to indicate that we want <span class="caps">FIFO</span>.</p> <p>No problem. That&#8217;s an easy fix.</p> <pre class="rubycode"> def remove_from_queue @queue.shift end </pre> <p>Now the tests run clean:</p> <pre class="shell"> $ ruby test_f3dqueue.rb Started .. Finished in 0.001925 seconds. 2 tests, 3 assertions, 0 failures, 0 errors </pre> <h2>Proving that Running a Job Works</h2> <p>Now when I run a job, I need to show that the proper four methods are called once each and in the proper order. This is very straight forward using FlexMock.</p> <pre class="testcode"> def test_running_a_job_will_call_the_right_stuff_in_the_right_order job = flexmock("job") job.should_receive(:generate_geometry_and_grid).once.ordered job.should_receive(:partition_grid_and_initialize_flow).once.ordered job.should_receive(:run_flow_solver).once.ordered job.should_receive(:post_process_solution).once.ordered q = F3DQueue.new q.run(job) end </pre> <p>Uncommenting the body of <ins>run</ins> is all that is needed here:</p> <pre class="rubycode"> def run( job ) # $log.info 'Request being processed' job.generate_geometry_and_grid # $log.info 'Created Geometry' job.partition_grid_and_initialize_flow # $log.info 'Partitioned Grid' job.run_flow_solver # $log.info 'Flow Solver Completed' job.post_process_solution # $log.info 'Post process Completed' # $log.info 'Request completed' end </pre> <p>Test are now showing:</p> <pre class="shell"> 3 tests, 3 assertions, 0 failures, 0 errors </pre> <h2>Processing an Empty Queue</h2> <p>Ok, now it gets interesting. I want to show that attempting to process a job when the queue is empty will cause the process to sleep for the check queue interval.</p> <p>This is one spot where I changed the code to make it easier to test. It is difficult to test endless loops in unit tests (it tends to make the tests run a <em>bit</em> long), so I broke out the logic for a single pass through the loop into a method called <ins>process_one_job</ins>. We can then test this logic without dealing with the looping at the same time.</p> <p>Note: It is possible to test endless loops and an example will be given below. But it is slightly tricky and this allows us to concentrate on proving the logic.</p> <p>If there are no jobs to be processed, then all the code should do is sleep for a particular amount of time. We will locally mock out the <ins>sleep</ins> method on the queue object and insist that it will be called exactly once with the expected interval.</p> <pre class="testcode"> def test_processing_with_no_jobs_will_sleep_the_check_interval q = F3DQueue.new flexmock(q).should_receive(:sleep).once.with(F3DQueue::CHECK_QUEUE_INTERVAL) q.process_one_job end </pre> <p>Here is <ins>process_one_job</ins> with just two lines uncommented so that the test will pass.</p> <pre class="rubycode"> def process_one_job # execution_attempts = 0 job = remove_from_queue # begin # if job # run job # execution_attempts = 0 # sleep SERVER_RECOVERY_TIME # else sleep CHECK_QUEUE_INTERVAL # end # rescue # $log.warn 'An error occurred during execution' # $log.warn $ERROR_INFO # $log.debug $ERROR_POSITION # sleep SERVER_RECOVERY_TIME # if execution_attempts &gt; MAX_EXECUTION_ATTEMPTS # $log.error 'Too many failed execution_attempts: aborting' # raise # else # execution_attempts += 1 # retry # end # end end </pre> <p>There&#8217;s a lot of code still left commented in that method. Now we need a test to force us to uncomment more code.</p> <h2>Handling a Single Job</h2> <p>Ok, now what happens when a single job is in the queue. We will assume the happy path (i.e. no exceptions) so we expect <ins>run</ins> to be called with the queued object, and then a sleep with the recovery interval.</p> <p>A couple of things to note. First, we mock out AutoF3D again so that when we request something added to the queue, we control what kind of object is returned. We <em>could</em> return a mock object and then mock out the four methods that <ins>run</ins> will be calling.</p> <p>However, I chose a slightly different approach. AutoF3D is mocked so that it returns a simple symbol. Then I mock out the <ins>run</ins> method to do nothing (but it is expected to be called once). This is slightly controversial because I am actually mocking a method on the object under test. But the run method is fairly simple, and we know that <ins>run</ins> works because of our previous test, so in the end we get clearer and simpler code.</p> <p>Also note that the <ins>run</ins> and <ins>sleep</ins> methods mocks are ordered. This means <ins>run</ins> will be called first, then <ins>sleep</ins>.</p> <pre class="testcode"> def test_processing_with_a_single_job_will_run_the_job_and_pause_for_recovery q = F3DQueue.new flexmock(AutoF3D).should_receive(:new).once.and_return(:job) flexmock(q).should_receive(:run).once.with(:job).ordered flexmock(q).should_receive(:sleep).once.with(F3DQueue::SERVER_RECOVERY_TIME).ordered q.add_to_queue(:a, :b, :c) q.process_one_job end </pre> <p>Now we get to uncomment even more lines in <ins>process_one_job</ins>.</p> <pre class="rubycode"> def process_one_job # execution_attempts = 0 job = remove_from_queue # begin if job run job # execution_attempts = 0 sleep SERVER_RECOVERY_TIME else sleep CHECK_QUEUE_INTERVAL end # rescue # $log.warn 'An error occurred during execution' # $log.warn $ERROR_INFO # $log.debug $ERROR_POSITION # sleep SERVER_RECOVERY_TIME # if execution_attempts &gt; MAX_EXECUTION_ATTEMPTS # $log.error 'Too many failed execution_attempts: aborting' # raise # else # execution_attempts += 1 # retry # end # end end </pre> <p>That just leaves the error handling code to be uncommented. So that will be next.</p> <h2> Handling a Job With Errors</h2> <p>Now we want to test the case where processing a job will return an exception. This test exercise the exception recovery code in the original code base. The technique is similar to the last test, but this time we specify two mock calls for <ins>run</ins>. The first time <ins>run</ins> will return an exception. The second time it is called, it will complete normally.</p> <p>Notice that we have ordered <ins>run</ins> and <ins>sleep</ins> so that they interleave execution with each other.</p> <pre class="testcode"> def test_if_a_job_fails_retry_after_recovery_time q = F3DQueue.new flexmock(AutoF3D).should_receive(:new).once.and_return(:job) flexmock(q).should_receive(:run).once.with(:job).and_raise(RuntimeError).ordered flexmock(q).should_receive(:sleep).once.with(F3DQueue::SERVER_RECOVERY_TIME).ordered flexmock(q).should_receive(:run).once.with(:job).ordered flexmock(q).should_receive(:sleep).once.with(F3DQueue::SERVER_RECOVERY_TIME).ordered q.add_to_queue(:a, :b, :c) q.process_one_job end </pre> <p>I was showing this test code to one of my coworkers and they were a little surprised that the second expectation on <ins>run</ins> didn&#8217;t override the first expectation. FlexMock is explicitly designed to allow you to stack expectations like this. When searching for an expectation during mocking, FlexMock will use the first one matching one if finds. When an expectation has been used its designated number of times (in the above test, the <ins>once</ins> method designates that the expectation should only be used once), FlexMock will begin to use matching expectations that are defined later.</p> <p>The upshot is this is that it is easy to define mock behavior for multiple calls to the same method.</p> <p>Here&#8217;s the latest <ins>process_one_job</ins> method with some more lines uncommented. We are getting close to the end with this one.</p> <pre class="rubycode"> def process_one_job # execution_attempts = 0 job = remove_from_queue begin if job run job # execution_attempts = 0 sleep SERVER_RECOVERY_TIME else sleep CHECK_QUEUE_INTERVAL end rescue # $log.warn 'An error occurred during execution' # $log.warn $ERROR_INFO # $log.debug $ERROR_POSITION sleep SERVER_RECOVERY_TIME # if execution_attempts &gt; MAX_EXECUTION_ATTEMPTS # $log.error 'Too many failed execution_attempts: aborting' # raise # else # execution_attempts += 1 retry # end end end </pre> <h2>Processing Jobs that Continually Fail</h2> <p>Finally we test the case where the job will continually raise an exception until the error recovery code gives up and passes the exception on to the caller. I didn&#8217;t bother ordering the run/sleep calls here, making it easy to just specify that each are called four times. I believe that the previous test adequately specified interleaving.</p> <p>I used a RuntimeError for my testing. If you have a specific error in mind, you might want to test explicitly for it. Generally raising the most general error you intend to handle is a good way of testing the boundry conditions on your rescue clause.</p> <pre class="testcode"> def test_too_many_failures_will_pass_along_exception q = F3DQueue.new flexmock(AutoF3D).should_receive(:new).once.and_return(:job) flexmock(q).should_receive(:run).with(:job).and_raise(RuntimeError.new("XYZZY")).times(4) flexmock(q).should_receive(:sleep).with(F3DQueue::SERVER_RECOVERY_TIME).times(4) q.add_to_queue(:a, :b, :c) ex = assert_raise RuntimeError do q.process_one_job end assert_equal "XYZZY", ex.message end </pre> <p>Note that the exception needs to be raised four times. I suspect this is a bug in the error handling logic. I left the logic as is and just made sure the test will pass. The code base specifies a retry count of &#8220;2&#8221;. This seems to imply that we try <ins>run</ins> twice, or perhaps three times (if the initail attempt doesn&#8217;t count as a retry). In any case, four times seems too much.</p> <p>So, here is the code for <ins>process_one_job</ins> with most of its lines uncommented.</p> <pre class="rubycode"> def process_one_job execution_attempts = 0 job = remove_from_queue begin if job run job # execution_attempts = 0 sleep SERVER_RECOVERY_TIME else sleep CHECK_QUEUE_INTERVAL end rescue # $log.warn 'An error occurred during execution' # $log.warn $ERROR_INFO # $log.debug $ERROR_POSITION sleep SERVER_RECOVERY_TIME if execution_attempts &gt; MAX_EXECUTION_ATTEMPTS # $log.error 'Too many failed execution_attempts: aborting' raise else execution_attempts += 1 retry end end end </pre> <p>Again note that this test surfaced a (rather minor) bug. There is an extra assignment that clears the execution attempt counter after a successful run of <ins>job</ins>. Since a successful run will exit the loop, clearing it has no effect (unless it is the sleep command that fails, that would be an interesting test scenario).</p> <p>Since we haven&#8217;t shown the test results for a while, here&#8217;s how we stand at this point:</p> <pre class="shell"> 7 tests, 5 assertions, 0 failures, 0 errors </pre> <h2>Processing Multiple Jobs</h2> <p>Now we know that we can handle a single job successfully. Now let&#8217;s make sure that we can handle multiple jobs. Remember that we broke <ins>process</ins> into two methods: <ins>process_one_job</ins> and a much shorter <ins>process</ins> that will call <ins>process_one_job</ins> in a loop.</p> <p>Here&#8217;s what the original <ins>process</ins> method is looking like at the moment:</p> <pre class="rubycode"> def process # loop do # end end </pre> <p>We pulled out its guts and left the still commented loop there. We haven&#8217;t even bothered to have it call <ins>process_one_job</ins> yet. So let&#8217;s write a test that will force us to fix that.</p> <p>We will just mock out process_one_job so that it must be called 10 times. On the eleventh call it throws a symbol that we catch in the test. Throwing a symbol is the trick that breaks us out of the infinite loop. By throwing a symbol (rather than raising an error), we don&#8217;t interact with the error handling logic of the code under test.</p> <p>This is actually the trick refereced earlier. By breaking the body of the loop into a separate method, we only have to use this trick once rather than on each of the process job tests.</p> <pre class="testcode"> def test_process_calls_process_one_job_in_a_loop q = F3DQueue.new flexmock(q).should_receive(:process_one_job).times(10) flexmock(q).should_receive(:process_one_job).and_return { throw :done } assert_throws(:done) do q.process end end </pre> <p>To get this to pass, we implement the <ins>process</ins> method as follows:</p> <pre class="rubycode"> def process loop do process_one_job end end </pre> <h2>Threading Issues</h2> <p>Finally we need to make sure a thread is started. Here is another place I changed the code to make testing easier. The original code base started a thread in the initializer of the object. This means that <strong>every</strong> F3DQueue object ran in its own thread. This would means every test would have to deal with multithread issues. Yuck!</p> <p>I changed the code so that a thread is started only when explicitly calling the start method. I like this better for real object anyways. Although it is an extra step, it gives you more control about when the threads are started. If you really want to start a thread at object creation, you can just say:</p> <pre><code>queue = F3DQueue.new.start</code></pre> <p>Since I really don&#8217;t want to start a Thread in the test (I just want to make sure that the Thread.new method is called), I mock out Thread.new so that it must be called once and when called will execute the given block.</p> <p>I then mock out the process method to that it must be called once. The combination of these two mocks will ensure that <ins>start</ins> will start a new thread that calls <ins>process</ins>.</p> <p>And finally, I ensure that the return value of <ins>start</ins> will be the queue object. This makes sure that the F3DQueue.new.start idiom works.</p> <pre class="testcode"> def test_start_will_start_a_process_thread q = F3DQueue.new flexmock("thread", Thread).should_receive(:new).with(Proc).once. and_return { |block| block.call } flexmock(q).should_receive(:process).once return_value = q.start assert_equal q, return_value end </pre> <p>And is is the little <ins>start</ins> method that needed to be written for the test. The Thread.new line is moved from the <ins>initialize</ins> method to here.</p> <pre class="rubycode"> def start Thread.new do process end self end </pre> <p>Here&#8217;s our final test run:</p> <pre class="shell"> 9 tests, 7 assertions, 0 failures, 0 errors </pre> <h2>Code Coverage</h2> <p>We know that <span class="caps">TDD</span> gives pretty code code coverage stats out of the box. How did our &#8220;Comment-out First&#8221; approach do with regards to code coverage?</p> <p>Here is the RCov report:</p> <pre class="shell"> +----------------------------------------------------+-------+-------+--------+ | File | Lines | LOC | COV | +----------------------------------------------------+-------+-------+--------+ |AutoF3D.rb | 5 | 2 | 100.0% | |f3dqueue.rb | 82 | 53 | 100.0% | |test_f3dqueue.rb | 100 | 76 | 100.0% | +----------------------------------------------------+-------+-------+--------+ |Total | 187 | 131 | 100.0% | +----------------------------------------------------+-------+-------+--------+ 100.0% 3 file(s) 187 Lines 131 LOC </pre> <p>Wow! 100% on the first try.</p> <h2>Final Code Samples</h2> <p>You can find the final versions of the F3DQueue object and its tests here:</p> <ul> <li><a href="http://wikis.onestepback.org/OSB/page/show/FinalF3DQueueCode">F3DQueue Code</a></li> <li><a href="http://wikis.onestepback.org/OSB/page/show/FinalF3DQueueTestCode">F3DQueue Test Code</a></li> </ul> <h2>Future Directions</h2> <p>Now that the F3DQueue object is well testing, it is time to take a step back and think about the overall design of the class. There are a couple of things that stick out in my mind about this code.</p> <h3>(1) First Item</h3> <p>We did a lot of mocking on the F3DQueue object itself while it was being testing. Although a valid technique, you must be careful so that you don&#8217;t end up just testing your own mocks. What it <em>does</em> indicate is that the object you are testing might be trying to do too many things. Perhaps the class needs to be broken up into small classes, or perhaps some functionality needs to move into other classes.</p> <p>With this in mind, the <ins>run</ins> method seems to know an awful lot about the workings of an Auto3D job object. It seems a bit out of place. Why don&#8217;t we move the <ins>run</ins> method to the job itself. Moving <ins>run</ins> into the Auto3D job object would allow us to write the following code fragment (in the <ins>process_one_job</ins> method):</p> <pre class="rubycode"> ... job = remove_from_queue begin if job job.run # was: run job sleep SERVER_RECOVERY_TIME ... </pre> <p>Now, our queue class is one method shorter and is just concerned with the scheduling of the jobs and not the details of running the job itself. This is good &#8230;</p> <p>Except for the following little piece of code, which leads us into the second thing that bothered me:</p> <pre class="rubycode"> def add_to_queue(modelLoc, params, gridFile) autoF3D = AutoF3D.new(modelLoc, params, gridFile) @queue.push autoF3D end </pre> <h3>(2) Second Item</h3> <p>Here we have direct knowledge of the AutoF3D class. If we remove the reference to AutoF3D, then our queue will suddenly become much more general, and usable in situations where we might want to process a different kind of job.</p> <p>I would recommend changing the above code to:</p> <pre class="rubycode"> def add_to_queue(job) @queue.push job end </pre> <p>This does mean that adding a job to the queue would now have to create the job object explicitly. So, instead of:</p> <pre> queue.add_to_queue(loc, param, grid) </pre> <p>you would have to write:</p> <pre> queue.add_to_queue(new AutoF3D.new(loc, param, grid)) </pre> <p>If you don&#8217;t like to manually create an AutoF3D object all the time (and I don&#8217;t), then the following solution is an easy fix to that:</p> <pre class="rubycode"> queue = F3DQueue.new def queue.add_job(loc, params, grid) add_to_queue(AutoF3D.new(loc, params, grid)) end </pre> <p>The more traditionally minded of us might want to just subclass the F3DQueue class and add the <ins>add_job</ins> method in the subclass rather than in the singleton class. That works too. Either way, it is easy to do.</p> <h2>Recap</h2> <p>I hope this was useful for you. Here is a recap of some of the important ideas from this exercise:</p> <ul> <li>Comment-First is not a bad way to handle legacy code.</li> </ul> <ul> <li>Test scenarios, not methods. Note that I didn&#8217;t just pick a method in F3DQueue and write a single test for it. I choose scenarios that would exercise different sections of the code base. Start with the simple (e.g. a Job that Doesn&#8217;t Fail). Then pick increasing harder scenarios (e.g. &#8220;a Job that Fails Once&#8221;, &#8220;a Job that Fails Multiple Times&#8221;).</li> </ul> <ul> <li>Don&#8217;t be afraid to refactor to make testing easier. Breaking out <ins>process_one_job</ins> was a great idea that not only made testing much easier, but made the code easier to read.</li> </ul> <ul> <li>The &#8220;Use Symbols as Cheap Mocks&#8221; is an idea I stole from Stu Halloway in his &#8220;Refactoring of the Week&#8221; presentation. If a method takes arguments that you don&#8217;t want to deal with, try passing in symbols. If the arguments aren&#8217;t used, the symbols work great. If an argument is actually used, the error message will identify the symbol at fault. At that point, just replace the symbol with the appropriate mock. This technique save you lots of time and makes the tests easier to read.</li> </ul> <ul> <li>If you want to break out of an infinite loop in the code under test, throw a symbol from your mocks and catch it in your test. This generally doesn&#8217;t interfere with any exception handling code in your code under test.</li> </ul> <ul> <li>Always take a step back and look for ways of improving the code. A well tested module is fairly easy to change with confidence. Don&#8217;t be afraid to improve things.</li> </ul> <h2>More Samples</h2> <p>Do you have a bit of code that you are having trouble testing? If so, go ahead and send it to me. If your code is interesting enough, I&#8217;ll take a look at it and post the results here (so don&#8217;t send anything you aren&#8217;t willing to see published in this blog). I can&#8217;t look at everything, but I&#8217;ll try to find some interesting examples.</p>
Dependency Injection in One Sentence
<p style="padding-left:3em;"><em>Condensing thoughts down to one sentence &#8230;</em></p> <h2>In One Sentence &#8230;</h2> <p>So I was asked this question in IM today:</p> <p style="padding-left:3em;"><em>If you had one sentence to explain to a Java programmer why Dependency Injection is rarely necessary in Ruby, what would it be?</em></p> <p>Wow, one sentence! After some thought, here&#8217;s what I sent back:</p> <p style="padding-left:3em;"><em>Dependency injection provides vital flexibility in Java and unneeded overhead in Ruby.</em></p> <p>Anyone have other suggestions?</p>
What Should flexmock(real_obj) Return?
<p style="padding-left:3em;"><em>Bruce Williams asked this question at RailsConf, and I am soliciting feedback.</em></p> <h2>Background</h2> <p>First, a little background. There are two possibilities when calling <tt>flexmock()</tt>. First, you are creating a full mock object:</p> <pre> # Example 1 mock = flexmock("description") mock.should_receive(...) </pre> <p>A full mock fulfills two roles: (1) it is a target for <tt>should_receive</tt> to define expectations, and (2) it is a target for normal domain messages when testing.</p> <p>The other possibility is that you are creating a partial mock (i.e. a regular Ruby object with just a few mocked methods):</p> <pre> # Example 2 real_obj = RealObject.new proxy_mock = flexmock(real_obj, "description") proxy_mock.should_receive(...) </pre> <p>The object returned from the <tt>flexmock()</tt> method is actually a proxy object that can accept <tt>should_receive()</tt> messages to define the expectations, but does not handle normal domain messages. After all, we have a real object that that handles domain messages.</p> <h2>Partial Mocks</h2> <p>It is clear that when creating a partial mock using the non-block form of flexmock(real_obj), we must return the proxy, else there would be no way to add expectations. But the return value for the block form of flexmock is not so clear.</p> <p>Consider the following code:</p> <pre> # Example 3 real_obj = RealObject.new result = flexmock(real_obj) do |mock| mock.should_receive(...) end </pre> <p>Here the proxy object is passed as the block argument. All the expectation setup is done within the block. It is <em>very</em> tempting to write this code as:</p> <pre> # Example 4 result = flexmock(RealObject.new) do |mock| mock.should_receive(...) end </pre> <p>But here is the problem: in example 4 we no longer have a reference to the RealObject instance. The <tt>flexmock()</tt> method returns the proxy object, not the real object; just as it does in the non-block form.</p> <h2>Bruce&#8217;s Suggestions</h2> <p>Bruce suggested changing the block version of flexmock() to go ahead and return the real object. Since the proxy is used in the block, there is no real need for it outside the function. And, I will admit, example 4 is short and relatively clear, especially with those familiar with the <tt>returning</tt> idiom used in Rails.</p> <h2>The Dilemma</h2> <p>So here is my dilemma. Changing FlexMock so that example 4 works properly is attractive. And I suspect that the return value of flexmock(real_obj) is not ever used in a significant way in existing code, so backwards compatibility should be be only a minor concern. However, changing the return object based on whether or not the method has a block just seems &#8230; <em>wrong</em>.</p> <p>There is precedent for this. In the standard Ruby libraries <tt>open(fn)</tt> and <tt>open(fn) { ... }</tt> return different things (an open file for the former and the value of the block for the latter). I&#8217;ve never had problems with this behavior in open, so perhaps I am just being over sensitive here.</p> <p>I told Bruce I would blog the issue and consider the feedback received. So let me know what you think. Should <tt>flexmock()</tt> be modified to return the real_object when defining partial mocks using the block form?</p> <p>You can email me (jim@weirichhouse.org) or add a comment using the comments link below.</p>
FlexMock 0.6.0 Released
<em>FlexMock version 0.6.0 was just released over the weekend. You can read the release announcement below for all the new features and enhancements.</em> <hr size="2"></hr><p> FlexMock is a flexible mocking library for use in unit testing and behavior specification in Ruby. Version 0.6.0 introduces a number of API enhancements to make testing with mocks even easier than before. </p> <h2>New in 0.6.0</h2> <ul> <li>Better integration with Test::Unit (no need to explicitly include FlexMock::TestCase). </li> <li>Integration with RSpec (version 0.9.0 or later of RSpec is required). </li> <li>The <tt>flexmock</tt> method will now create both regular mocks and partial mocks. <pre> flexmock() # =&gt; a full mock flexmock(person) # =&gt; a partial mock based on person </pre> <p> (<tt>flexstub</tt> is still included for backwards compatibility). </p> </li> <li>Quick and simple mocks my now be created using an expectation hash. For example: <pre> flexmock(:foo =&gt; 10, :bar =&gt; &quot;Hello&quot;) </pre> <p> will create a mock with two methods, :foo and :bar,defined. :foo will return 10 when invoked, and :bar will return &quot;Hello&quot;. </p> </li> <li>The <tt>should_receive</tt> method will now allow multiple methods (with the same constraints) be defined in a single call. For example, the following declares that both :read and :write need to be called at least one time each on the mock object. <pre> flexmock.should_receive(:read, :write).at_least.once </pre> </li> <li><tt>should_recieve</tt> now will allow expectation hashes as arguments. This is similar to the list of methods, but allows each defined method to have its own return value. <pre> flexmock.should_receive(:name =&gt; &quot;John&quot;, :age =&gt; 32) </pre> </li> <li>In addition to using a block for defining constrains, constraints may now be applied directly to the return value of <tt>new_instances</tt>. Combined with the expectation hashes supported by <tt>should_receive</tt>, simple mocking scenarios have become much more succinct. For example: <pre> flexmock(Person).new_instances.should_receive(:name =&gt; &quot;John&quot;, :age =&gt; 32) </pre> </li> <li>Improved implementation, allowing for more flexible use and greater consistency between full mock and partial mocks. </li> <li>Version 0.6.0 also includes a fix for an incompatibility with some older versions of RCov. The FlexMock Rakefile now includes a RCov task (and we have 100% code coverage). </li> </ul> <h2>What is FlexMock?</h2> <p> FlexMock is a flexible framework for creating mock object for testing. When running unit tests, it is often desirable to use isolate the objects being tested from the &quot;real world&quot; by having them interact with simplified test objects. Sometimes these test objects simply return values when called, other times they verify that certain methods were called with particular arguments in a particular order. </p> <p> FlexMock makes creating these test objects easy. </p> <h3>Features</h3> <ul> <li>Easy integration with both Test::Unit and RSpec. Mocks created with the flexmock method are automatically verified at the end of the test or example. </li> <li>A fluent interface that allows mock behavior to be specified very easily. </li> <li>A &quot;record mode&quot; where an existing implementation can record its interaction with a mock for later validation against a new implementation. </li> <li>Easy mocking of individual methods in existing, non-mock objects. </li> <li>The ability to cause classes to instantiate test instances (instead of real instances) for the duration of a test. </li> </ul> <h3>Example</h3> <p> Suppose you had a Dog object that wagged a tail when it was happy. Something like this: </p> <pre> class Dog def initialize(a_tail) @tail = a_tail end def happy @tail.wag end end </pre> <p> To test the <tt>Dog</tt> class without a real <tt>Tail</tt> object (perhaps because real <tt>Tail</tt> objects activate servos in some robotic equipment), you can do something like this: </p> <p> require &#8216;test/unit&#8217; require &#8216;flexmock/test_unit&#8216; </p> <pre> class TestDog &lt; Test::Unit::TestCase def test_dog_wags_tail_when_happy tail = flexmock(&quot;tail&quot;) tail.should_receive(:wag).once dog = Dog.new(tail) dog.happy end end </pre> <p> FlexMock will automatically verify that the mocked tail object received the message <tt>wag</tt> exactly one time. If it doesn&#8217;t, the test will not pass. </p> <p> See the FlexMock documentation at <a href="http://flexmock.rubyforge.org">flexmock.rubyforge.org</a> for details on specifying arguments and return values on mocked methods, as well as a simple technique for mocking tail objects when the Dog class creates the tail objects directly. </p> <h2>Availability</h2> <p> You can make sure you have the latest version with a quick RubyGems command: </p> <pre> gem install flexmock (you may need root/admin privileges) </pre> <p> Otherwise, you can get it from the more traditional places: </p> <table> <tr><td valign="top">Download:</td><td><a href="http://rubyforge.org/project/showfiles.php?group_id=170">rubyforge.org/project/showfiles.php?group_id=170</a> </td></tr> </table> <p> You will find documentation at: <a href="http://flexmock.rubyforge.org">flexmock.rubyforge.org</a>. </p> <p> &#8212; Jim Weirich </p>
Extended FlexMock Example Using Google4R
<em> I recently helped a friend use FlexMock to do some testing on code that was written ot use the Google4R checkout APIs. I thought it might be interesting to share some of the details here. Note that this code uses the recently released FlexMock version 0.6.0. </em> <p> Google4R is a simple Ruby wrapper around the Google APIs. In this extended example, we will use FlexMock to test software that uses the Google APIs, without every communicating with Google itself. </p> <h2>Purchase.rb</h2> <p> Here is the bit of code that we will be testing&#8230; </p> <pre> require 'google4r/checkout' require 'item' class Purchase def initialize(config) @frontend = Frontend.new(config) @frontend.tax_table_factory = TaxTableFactory.new end # Purchase the +quantity+ items identified by +item_id+. Return the # confirmation page URL. def purchase(item_id, quantity=1) item = Item.find(item_id) checkout = @frontend.create_checkout_command checkout.cart.create_item do |cart_item| cart_item.name = item.name cart_item.description = item.description cart_item.unit_price = item.unit_price cart_item.quantity = quantity end response = checkout.send_to_google_checkout response.redirect_url end end </pre> <p> <tt>FrontEnd</tt> is a Google4R class that provides a lot of the front end work for talking to the Google APIs. The config object given to the Purchase initializer is simply a hash of values defining the merchant_id, merchant_key and sandbox flag. To use the real Google checkout APIs, you will need to obtains a merchant id and key from Google. Since we will be mocking the Google interaction, we can use dummy values in our test. </p> <p> The tax table factory is required by the Google4R software. We provide the following simplified one. Read the Google API documents for more information. </p> <pre> class TestTaxTableFactory def effective_tax_tables_at(time) tax_free_table = TaxTable.new(false) tax_free_table.name = &quot;default table&quot; tax_free_table.create_rule do |rule| rule.area = UsCountryArea.new(UsCountryArea::ALL) rule.rate = 0.0 end return [tax_free_table] end end </pre> <p> <tt>Item</tt> is simply an ActiveRecord class that we are using to hold our purchase item information. It should respond to the <tt>name</tt>, <tt>description</tt> and <tt>unit_price</tt> messages. </p> <h2>Testing Without Using External Resources</h2> <p> Our first test attempt will be to run the <tt>purchase</tt> method without talking to either the live Google web services, or hitting an actual ActiveRecord database. </p> <h3>Mocking Active Record</h3> <p> The ActiveRecord part is easy to mock. The following will handle it: </p> <pre> flexmock(Item).should_receive(:find).with(1).and_return( flexmock(&quot;guitar&quot;, :name =&gt; &quot;Deschutes&quot;, :description =&gt; &quot;Deschutes model Guitar&quot;, :unit_price =&gt; Money.new(2400.00))) </pre> <p> We have mocked out the <tt>find</tt> method on <tt>Item</tt> so that whenever we call find with an integer argument of 1, we will return a mock item that will report its name, description and unit_price. This gives us