= Flex Mock -- Making Mock Easy

FlexMock is a simple, but flexible, mock object library for Ruby unit
testing.

Version :: 0.5.1

= Links

<b>Documents</b>   :: http://onestepback.org/software/flexmock
<b>RubyGems</b>    :: Install with: <b>gem install flexmock</b>
<b>Download</b>    :: Download from RubyForge at http://rubyforge.org/frs/?group_id=170

== Installation

You can install FlexMock with the following command.

 $ gem install flexmock

== Simple Example

We have a data acquisition class (+TemperatureSampler+) that reads a
temperature sensor and returns an average of 3 readings.  We don't
have a _real_ temperature to use for testing, so we mock one up with a
mock object that responds to the +read_temperature+ message.

Here's the complete example:

  require 'test/unit'
  require 'flexmock'

  class TemperatureSampler
    def initialize(sensor)
      @sensor = sensor
    end

    def average_temp
      total = (0...3).collect { @sensor.read_temperature }.inject { |i, s| i + s }
      total / 3.0
    end
  end

  class TestTemperatureSampler < Test::Unit::TestCase
    include FlexMock::TestCase

    def test_temperature_sampler
      sensor = flexmock("temp")
      sensor.should_receive(:read_temperature).times(3).and_return(10, 12, 14)

      sampler = TemperatureSampler.new(sensor)
      assert_equal 12, sampler.average_temp

      # NOTE:
      # all mocks created by the flexmock method will be
      # automatically verified during the test teardown.
    end
  end

== Quick Reference

=== Expectation Declarators

Expectation declarators are used to specify the expectations placed
upon received method calls.  The following declarators may be used to
create the proper expectations on a FlexMock object.

* <b><tt>should_receive(<em>symbol</em>)</tt></b> -- Declares that a
  message named <em>symbol</em> will be sent to the mock object.
  Further refinements on this expected message (called an expectation)
  may be chained to the +should_receive+ call.

* <b><tt>should_expect</tt></b> -- Creates a mock recording object
  that will translate received method calls into mock expectations.
  The recorder is passed to a block supplied with the +should_expect+
  method.  See examples below.

* <b><tt>with(<em>arglist</em>)</tt></b> -- Declares that this
  expectation matches messages that match the given argument list.
  The <tt>===</tt> operator is used on a argument by argument basis to
  determine matching.  This means that most literal values match
  literally, class values match any instance of a class and regular
  expression match any matching string (after a +to_s+ conversion).
  See argument validators (below) for details on argument validation
  options.

* <b><tt>with_any_args</tt></b> -- Declares that this expectation
  matches the message with any argument (default)

* <b><tt>with_no_args</tt></b> -- Declares that this expectation
  matches messages with no arguments

* <b><tt>and_return(<em>value, ...</em>)</tt></b> -- Declares 
  that the message will return the given value.
  * If a single value is given, it will be returned for all matching calls.
  * If multiple values are given, they will be returned in sequence
    for each successive matching calls.  The last value will be 
    repeatably returned if the number of matching calls exceeds the
    number of values.
  * If a block is given, its yielded value will be returned. (the 
    block will receive all the arguments given to the mocked method)
  * The default return value is nil. 

* <b><tt>returns(<em>value, ...</em>)</tt></b> -- Alias for
  <tt>and_return</tt>.

* <b><tt>returns { |args| code ... }</tt></b> -- Declares that the
  message will return whatever the block calculates.  The actual
  arguments in the message will be passed to the block.

* <b><tt>zero_or_more_times</tt></b> -- Declares that the message is
  may be sent zero or more times (default, equivalent to
  <tt>at_least.never</tt>).

* <b><tt>once</tt></b> -- Declares that the message is only sent once.
  <tt>at_least</tt> / <tt>at_most</tt> modifiers are allowed.

* <b><tt>twice</tt></b> -- Declares that the message is only sent
  twice.  <tt>at_least</tt> / <tt>at_most</tt> modifiers are allowed.

* <b><tt>never</tt></b> -- Declares that the message is never sent.
  <tt>at_least</tt> / <tt>at_most</tt> modifiers are allowed.

* <b><tt>times(<em>n</em>)</tt></b> -- Declares that the message is
  sent <em>n</em> times.  <tt>at_least</tt> / <tt>at_most</tt>
  modifiers are allowed.

* <b><tt>at_least</tt></b> -- Modifies the immediately following
  message count declarator so that it means the message is sent at
  least that number of times.  E.g. <tt>at_least.once</tt> means the
  message is sent at least once during the test, but may be sent more
  often.  Both <tt>at_least</tt> and <tt>at_most</tt> may be specified
  on the same expectation.

* <b><tt>at_most</tt></b> -- Similar to <tt>at_least</tt>, but puts an
  upper limit on the number of messages.  Both <tt>at_least</tt> and
  <tt>at_most</tt> may be specified on the same expectation.

* <b><tt>ordered</tt></b> -- Declares that the message is ordered and
  is expected to be received in a certain position in a sequence of
  messages.  The message should arrive after and previously declared
  ordered messages and prior to any following declared ordered
  messages.  Unordered messages are ignored when considering the
  message order.

* <b><tt>ordered(<em>group</em>)</tt></b> -- Declare that the given
  method belongs to an order group.  Methods within the group may be
  received in any order.  Ordered messages outside the group must be
  received either before or after the grouped messages.

  For example, in the following, messages +flip+ and +flop+ may be
  received in any order (because they are in the same group), but must
  occur strictly after +start+ but before +end+.  The message
  +any_time+ may be received at any time because it is not ordered.
    
        m = FlexMock.new
        m.should_receive(:any_time)
        m.should_receive(:start).ordered
        m.should_receive(:flip).ordered(:flip_flop_group)
        m.should_receive(:flop).ordered(:flip_flop_group)
        m.should_receive(:end).ordered
    
=== Argument Validation

The values passed to the +with+ declarator determine the criteria for
matching expectations.  The first expectation found that matches the
arguments in a mock method call will be used to validate that mock
method call.

The following rules are used for argument matching:

* A +with+ parameter that is a class object will match any actual
  argument that is an instance of that class.

  Examples:

     with(Integer)     will match    f(3)

* A regular expression will match any actual argument that matches the
  regular expression.  Non-string actual arguments are converted to
  strings via +to_s+ before applying the regular expression.

  Examples:

    with(/^src/)      will match    f("src_object")
    with(/^3\./)      will match    f(3.1415972)

* Most other objects will match based on equal values.

  Examples:

      with(3)         will match    f(3)
      with("hello")   will match    f("hello")
  
* If you wish to override the default matching behavior and force
  matching by equality, you can use the FlexMock.eq convenience
  method.  This is mostly used when you wish to match class objects,
  since the default matching behavior for class objects is to match
  instances, not themselves.

  Examples:

      with(eq(Integer))             will match       f(Integer)
      with(eq(Integer))             will NOT match   f(3)

  Note: If you do not use the FlexMock::TestCase Test Unit integration
  module, or the FlexMock::ArgumentTypes module, you will have to
  fully qualify the +eq+ method:

      with(FlexMock.eq(Integer))    will match       f(Integer)
      with(FlexMock.eq(Integer))    will NOT match   f(3)

* If you wish to match _anything_, then use the <tt>FlexMock.any</tt>
  method in the with argument list.

  Examples (assumes either the FlexMock::TestCase or
  FlexMock::ArgumentTypes mix-ins has been included):

      with(any)             will match       f(3)
      with(any)             will match       f("hello")
      with(any)             will match       f(Integer)
      with(any)             will match       f(nil)

* If you wish to specify a complex matching criteria, use the
  <tt>FlexMock.on(&block)</tt> with the logic contained in the block.

  Examples (assumes FlexMock::ArguementTypes has been included):

      with(on { |arg| (arg % 2) == 0 } )

  will match any even integer.

=== Stubbing Behavior in Existing Objects

Sometimes it is useful to mock the behavior of one or two methods in an
existing object without changing the behavior of the rest of the object. By
using the +flexstub+ method, tests can now do exactly that.

For example, suppose that a Dog object uses a Woofer object to
bark. The code for Dog looks like this (we will leave the code for
Woofer to your imagination):

  class Dog
    def initialize
      @woofer = Woofer.new
    end
    def bark
      @woofer.woof
    end
  end

Now we want to test Dog, but using a real Woofer object in the test is
a real pain (why? ... well because Woofer plays a sound file of a dog
barking, and that's really annoying during testing).

So, how can we create a Dog object with mocked Woofer?  All we need to
do is stub out the +new+ method of the Woofer class object and tell to
to return anything we want.

Here's the test code:

  class TestDogBarking < Test::Unit::TestCase
    include FlexMock::TestCase

    # Setup the tests by stubbing the +new+ method of 
    # Woofer and return a mock woofer.
    def setup
      flexstub(Woofer).should_receive(:new).and_return {
        flexmock("woofer") do |mock|
          mock.should_receive(:woof).and_return(:grrrr)
        end
      }
    end

    def test_bark
      assert_equal :grrrr, @dog.bark
    end
  end

The nice thing about stub is that after the test is over, the stubbed
out methods are returned to their normal state.  Outside the test
everything is back to normal.

The stub technique was inspired by the +Stuba+ library in the +Mocha+
project.

=== Stubbing Behavior in All Instances Created by a Class Object

Sometimes you want to stub all instances created by a class object.
For example, you might wish to work with Connection objects that have
their "send" method stubbed out.  However, the code under test creates
connections dynamically, so you can't stub them before the test is
run.

One approach is to stub the "new" method on the class object.  The
stubbed implementation of "new" would create a mock object to be
returned as the value of "new".  But since your stubbed implementation
of "new" has no access to the original behavior of new, you can't
really create stubs.

The <tt>any_instance</tt> method allows you to easily add stub
expectations to objects created by new.  Here's the Connection example
using <tt>any_instance</tt>:

      def test_connections
        flexstub(Connection).any_instance do |new_con|
          new_con.should_receive(:send).and_return(0)
        end
        connection = Connection.new
        connection.send    # This calls the stubbed version of send.
      end

Note that FlexMock adds the stub expectations after the original +new+
method has completed.  If the original version of +new+ yields the
newly created instance to a block, that block will get an unstubbed
version of the object.

=== Class Interception

<b>NOTE:</b> :: 
  <em>Class Interception is now deprecated. It only worked in a
  small number of cases. See the "Mocking Existing Objects"
  example above for a much better approach to the same problem. 
  Version 0.5.x will be the last version of FlexMock that supports the
  Class Interception API.</em>

FlexMock now supports simple class interception. For the duration of a test, a
mock class take the place of a named class inside the class to be tested.

Example:

Suppose we are testing class Foo, and Foo uses Bar internally.  We
would like for Bar.new to return a mock object during the test.

   def test_foo_with_an_intercepted_bar
     my_mock = flexmock("my_mock").should_receive(....).mock
     intercept(Bar).in(Foo).with(my_mock.mock_factory)

     bar = Bar.new
     bar.do_something
   end

== Examples

=== Expect multiple queries and a single update

The queries my have any arguments.  The update must have a specific
argument of 5.

   class TestDb
     include FlexMock::TestCase         

     def test_db
       db = flexmock('db')
       db.should_receive(:query).and_return([1,2,3])
       db.should_receive(:update).with(5).and_return(nil).once
       # test code here
     end
   end

=== Expect all queries before any updates

(This and following examples assume that the FlexMock::TestCase module
is being used.)

All the query message must occur before any of the update messages.

   def test_query_and_update
     db = flexmock('db')
     db.should_receive(:query).and_return([1,2,3]).ordered
     db.should_recieve(:update).and_return(nil).ordered
     # test code here
   end

=== Expect several queries with different parameters

The queries should happen after startup but before finish.  The
queries themselves may happen in any order (because they are in the
same order group).  The first two queries should happen exactly once,
but the third query (which matches any query call with a four
character parameter) may be called multiple times (but at least once).
Startup and finish must also happen exactly once.

Also note that we use the +with+ method to match different argument
values to figure out what value to return.

   def test_ordered_queries
     db = flexmock('db')
     db.should_receive(:startup).once.ordered
     db.should_receive(:query).with("CPWR").and_return(12.3).
       once.ordered(:queries)
     db.should_receive(:query).with("MSFT").and_return(10.0).
       once.ordered(:queries)
     db.should_receive(:query).with(/^....$/).and_return(3.3).
       at_least.once.ordered(:queries)
     db.should_receive(:finish).once.ordered
     # test code here
   end

=== Same as above, but using the Record Mode interface

The record mode interface offers much the same features as the
+should_receive+ interface introduced so far, but it allows the
messages to be sent directly to a recording object rather than be
specified indirectly using a symbol. 

   def test_ordered_queries_in_record_mode
     db = flexmock('db')
     db.should_expect do |rec|
       rec.startup.once.ordered
       rec.query("CPWR") { 12.3 }.once.ordered(:queries)
       rec.query("MSFT") { 10.0 }.once.ordered(:queries)
       rec.query("^....$/) { 3.3 }.at_least.once.ordered(:queries)
       rec.finish)once.ordered
     end
     # test code here using +db+.
   end

=== Using Record Mode to record a known, good algorithm for testing

Record mode is nice when you have a known, good algorithm that can use
a recording mock object to record the steps.  Then you compare the
execution of a new algorithm to behavior of the old using the recorded
expectations in the mock.  For this you probably want to put the
recorder in _strict_ mode so that the recorded expectations use exact
matching on argument lists, and strict ordering of the method calls.

<b>Note:</b> This is most useful when there are no queries on the mock
objects, because the query responses cannot be programmed into the
recorder object.

  def test_build_xml
    builder = flexmock('builder')
    builder.should_expect do |rec|
      rec.should_be_strict
      known_good_way_to_build_xml(rec)  # record the messages
    end
    new_way_to_build_xml(builder)       # compare to new way
  end

=== Expect multiple calls, returning a different value each time

Sometimes you need to return different values for each call to a
mocked method.  This example shifts values out of a list for this
effect.

   def test_multiple_gets
     file = flexmock('file')
     file.should_receive(:gets).with_no_args.
        and_return("line 1\n", "line 2\n")
     # test code here
   end

=== Ignore uninteresting messages

Generally you need to mock only those methods that return an
interesting value or wish to assert were sent in a particular manner.
Use the +should_ignore_missing+ method to turn on missing method
ignoring.

   def test_an_important_message
     m = flexmock('m')
     m.should_recieve(:an_important_message).and_return(1).once
     m.should_ignore_missing
     # test code here
   end

<b>Note:</b> The original +mock_ignore_missing+ is now an alias for
+should_ignore_missing+.

== Classic +mock_handle+ Interface

FlexMock still supports the simple +mock_handle+ interface used in the
original version of FlexMock.  +mock_handle+ is equivalent to the
following:

  def mock_handle(sym, expected_count=nil, &block)
    self.should_receive(sym).times(expected_count).returns(&block)
  end

== Other Mock Objects

ruby-mock      :: http://www.b13media.com/dev/ruby/mock.html
test-unit-mock :: http://www.deveiate.org/code/Test-Unit-Mock.shtml
mocha/stubba   :: http://mocha.rubyforge.org/

== License

Copyright 2003, 2004, 2005, 2006 by Jim Weirich (jim@weirichhouse.org).
All rights reserved.

Permission is granted for use, copying, modification, distribution,
and distribution of modified versions of this work as long as the
above copyright notice is included.

= Other stuff

Author::   Jim Weirich <jim@weirichhouse.org>
Requires:: Ruby 1.8.x or later

== Warranty

This software is provided "as is" and without any express or
implied warranties, including, without limitation, the implied
warranties of merchantibility and fitness for a particular
purpose.