FlexMock is a simple, but flexible, mock object library for Ruby unit testing.
0.9.0.beta.0
Install with: gem install flexmock
Download from RubyForge at rubyforge.org/frs/?group_id=3433 (pre 0.6.0 versions may be found at rubyforge.org/frs/?group_id=170)
You can install FlexMock with the following command.
$ gem install flexmock
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/test_unit' 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 def test_sensor_can_average_three_temperature_readings 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 end end
You can find an extended example of FlexMock in Google Example.
FlexMock integrates nicely with Test::Unit. Just require the
‘flexmock/test_unit’ file at the top of your test file. The
flexmock
method will be available for mock creation, and any
created mocks will be automatically validated and closed at the end of the
individual test.
Your test case will look something like this:
require 'flexmock/test_unit' class TestDog < Test::Unit::TestCase def test_dog_wags tail_mock = flexmock(:wag => :happy) assert_equal :happy, tail_mock.wag end end
NOTE: If you don’t want to automatically extend every TestCase with the flexmock methods and overhead, then require the ‘flexmock’ file and explicitly include the FlexMock::TestCase module in each test case class where you wish to use mock objects. FlexMock versions prior to 0.6.0 required the explicit include.
FlexMock also supports integration with the RSpec behavior specification framework. Starting with version 0.9.0 of RSpec, you will be able to say:
Spec::Runner.configure do |config| config.mock_with :flexmock end describe "Using FlexMock with RSpec" do it "should be able to create a mock" do m = flexmock(:foo => :bar) m.foo.should === :bar end end
If you wish to try this prior to the release of RSpec 0.9.0, check out the trunk of the RSpec subversion repository.
The flexmock
method is used to create mocks in various
configurations. Here’s a quick rundown of the most common options. See
FlexMock::MockContainer#flexmock
for more details.
mock = flexmock(“joe”)
Create a mock object named “joe” (the name is used in reporting errors).
mock = flexmock(:foo => :bar, :baz => :froz)
Create a mock object and define two mocked methods (:foo and :baz) that return the values :bar and :froz respectively. This is useful when creating mock objects with just a few methods and simple return values.
mock = flexmock(“joe”, :foo => :bar, :bar => :froz)
You can combine the mock name and an expectation hash in the same call to flexmock.
partial_mock = flexmock(real_object)
If you you give flexmock
a real object in the argument list,
it will treat that real object as a base for a partial mock object. The
return value m
may be used to set expectations. The
real_object should be used in the reference portion of the test.
partial_mock = flexmock(real_object, “name”, :foo => :baz)
Names and expectation hashes may be used with partial mocks as well.
partial_mock = flexmock(:base, real_string_object)
Since Strings (and Symbols for that matter) are used for mock names, FlexMock will not recognize them as the base for a partial mock. To force a string to be used as a partial mock base, proceed the string object in the calling sequence with :base.
partial_mock = flexmock(:safe, real_object) { |mock| mock.should_receive(…) }
When mocking real objects (i.e. “partial mocks”), FlexMock will add a handful of mock related methods to the actual object (see below for list of method names). If one or more of these added methods collide with an existing method on the partial mock, then there are problems.
FlexMock offers a “safe” mode for partial
mocks that does not add these methods. Indicate safe mode by passing the
symbol :safe as the first argument of flexmock. A block is
required when using safe mode (the partial_mock returned in safe mode
does not have a should_receive
method).
The methods added to partial mocks in non-safe mode are:
should_receive
new_instances
any_instance (note: deprecated)
mock
mock_teardown
mock_setup
mock = flexmock(…) { |mock| mock.should_receive(…) }
If a block is given to any of the flexmock
forms, the mock
object will be passed to the block as an argument. Code in the block can
set the desired expectations for the mock object.
mock_model = flexmock(:model, YourModel, …) { |mock| mock.should_receive(…) }
When given :model, flexmock() will return a pure mock (not a partial mock) that will have some ActiveRecord specific methods defined. YourModel should be the class of an ActiveRecord model. These predefined methods make it a bit easier to mock out ActiveRecord model objects in a Rails application. Other that the predefined mocked methods, the mock returned is a standard FlexMock mock object.
The predefined mocked methods are:
id – returns a unique ID for each mocked model.
to_params – returns a stringified version of the id.
new_record? – returns false.
errors – returns an empty (mocked) errors object.
is_a?(other) – returns true if other == YourModel.
instance_of?(class) – returns true if class == YourModel
kind_of?(class) – returns true if class is YourModel or one of its ancestors
class – returns YourModel.
NOTE: Versions of FlexMock
prior to 0.6.0 used flexstub
to create partial mocks. The
flexmock
method now assumes all the functionality that was
spread out between two different methods. flexstub
is still
available for backward compatibility.
Once a mock is created, you need to define what that mock should expect to
see. Expectation declarators are used to specify these expectations placed
upon received method calls. A basic expectation, created with the
should_receive
method, just establishes the fact that a method
may (or may not) be called on the mock object. Refinements to that
expectation may be additionally declared. FlexMock always starts with the most general
expectation and adds constraints to that.
For example, the following code:
mock.should_receive(:average).and_return(12)
Means that the mock will now accept method calls to an average
method. The expectation will accept any arguments and may be called any
number of times (including zero times). Strictly speaking, the
and_return
part of the declaration isn’t exactly a
constraint, but it does specify what value the mock will return when the
expectation is matched.
If you want to be more specific, you need to add additional constraints to your expectation. Here are some examples:
mock.should_receive(:average).with(12).once mock.should_receive(:average).with(Integer). at_least.twice.at_most.times(10). and_return { rand }
The following methods may be used to create and refine expectations on a mock object. See theFlexMock::Expectation for more details.
should_receive(method_name)
Declares that a message named method_name will be sent to the mock
object. Constraints on this expected message (called expectations) may be
chained to the should_receive
call.
should_receive(method_name1, method_name2, …)
Define a number of expected messages that have the same constraints.
should_receive(meth1 => result1, meth2 => result2, …)
Define a number of expected messages that have the same constrants, but return different values.
should_expect { |recorder| … }
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.
with(arglist)
Declares that this expectation matches messages that match the given
argument list. The ===
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.
with_any_args
Declares that this expectation matches the message with any argument (default)
with_no_args
Declares that this expectation matches messages with no arguments
and_return(value)
Declares that the expected message will return the given value.
and_return(value1, value2, …)
Declares that the expected message will return a series of values. Each invocation of the message will return the next value in the series. The last value will be repeatably returned if the number of matching calls exceeds the number of values.
and_return { |args, …| code … }
Declares that the expected message will return the yielded value of the block. The block will receive all the arguments in the message. If the message was provided a block, it will be passed as the last parameter of the block’s argument list.
returns( … )
Alias for and_return
.
and_raise(exception, *args)
Declares that the expected messsage will raise the specified exception. If
exception
is an exception class, then the raised exception
will be constructed from the class with new
given the supplied
arguments. If exception
is an instance of an exception class,
then it will be raised directly.
raises( … )
Alias for and_raise
.
and_throw(symbol)
and_throw(symbol, value)
Declares that the expected messsage will throw the specified symbol. If an optional value is included, then it will be the value returned from the corresponding catch statement.
throws( … )
Alias for and_throw
.
and_yield(values, …)
Declares that the mocked method will receive a block, and the mock will
call that block with the values given. Not providing a block will be an
error. Providing more than one and_yield
clause one a single
expectation will mean that subsquent mock method calls will yield the
values provided by the additional and_yield
clause.
yields( … )
Alias for and_yield( ... )
.
zero_or_more_times
Declares that the expected message is may be sent zero or more times
(default, equivalent to at_least.never
).
once
Declares that the expected message is only sent once. at_least
/ at_most
modifiers are allowed.
twice
Declares that the expected message is only sent twice.
at_least
/ at_most
modifiers are allowed.
never
Declares that the expected message is never sent. at_least
/
at_most
modifiers are allowed.
times(n)
Declares that the expected message is sent n times.
at_least
/ at_most
modifiers are allowed.
at_least
Modifies the immediately following message count constraint so that it
means the message is sent at least that number of times. E.g.
at_least.once
means the message is sent at least once during
the test, but may be sent more often. Both at_least
and
at_most
may be specified on the same expectation.
at_most
Similar to at_least
, but puts an upper limit on the number of
messages. Both at_least
and at_most
may be
specified on the same expectation.
ordered
Declares that the expected 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.
Normally ordering is performed only against calls in the same mock object. If the “globally” adjective is used, then ordering is performed against the other globally ordered method calls.
ordered(group)
Declare that the expected message belongs to an order group. Methods within an order group may be received in any order. Ordered messages outside the group must be received either before or after all of 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() 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
Normally ordering is performed only against calls in the same mock object. If the “globally” adjective is used, then ordering is performed against the other globally ordered method calls.
globally.ordered
globally.ordered(group_name)
When modified by the “globally” adjective, the mock call will be ordered against other globally ordered methods in any of the mock objects in the same container (i.e. same test). All the options of the per-mock ordering are available in the globally ordered method calls.
by_default
Marks the expectation as a default. Default expectations act as normal as long as there are no non-default expectations for the same method name. As soon as a non-default expectation is defined, all default expectations for that method name are ignored.
Default expectations allow you to setup a set of default behaviors for various methods in the setup of a test suite, and then override only the methods that need special handling in any given test.
mock
Expectation constraints always return the expectation so that the
constraints can be chained. If you wish to do a one-liner and assign the
mock to a variable, the mock
method on an expectation will
return the original mock object.
m = flexmock.should_receive(:hello).once.and_return("World").mock
NOTE: <em>Using mock when specifying a Demeter mock chain will return the last mock of the chain, which might not be what you expect.
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. This is true of all
the special argument matches (eq
, on
,
any
, hsh
and ducktype
).
with(FlexMock.eq(Integer)) with(FlexMock.on { code }) with(FlexMock.any) with(FlexMock.hsh(:tag => 3)) with(FlexMock.ducktype(:wag => "dog"))
If you wish to match a hash on some of its values, the FlexMock.hsh(…) method will work. Only specify the hash values you are interested in, the others will be ignored.
with(hsh(:run => true)) will match f(:run => true, :stop => false)
If you wish to match any object that responds to a certain set of methods, use the FlexMock.ducktype method.
with(ducktype(:to_str)) will match f("string") with(ducktype(:wag, :bark)) will match f(dog) (assuming dog implements wag and bark)
If you wish to match anything, then use the
FlexMock.any
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
FlexMock.on(&block)
with the logic contained in the block.
Examples (assumes FlexMock::ArgumentTypes has been included):
with(on { |arg| (arg % 2) == 0 } )
will match any even integer.
If you wish to match a method call where a block is given, add
Proc
as the last argument to with
.
Example:
m.should_receive(:foo).with(Integer,Proc).and_return(:got_block) m.should_receive(:foo).with(Integer).and_return(:no_block)
will cause the mock to return the following:
m.foo(1) { } => returns :got_block m.foo(1) => returns :no_block
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. If
you pass a real object to the flexmock
method, it will allow
you to use that real object in your test and will just mock out the one or
two methods that you specify.
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 def wag :happy 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
allow FlexMock to replace the bark
method.
Here’s the test code:
class TestDogBarking < Test::Unit::TestCase include FlexMock::TestCase # Setup the tests by mocking the +new+ method of # Woofer and return a mock woofer. def setup @dog = Dog.new flexmock(@dog, :bark => :grrr) end def test_dog assert_equal :grrr, @dog.bark # Mocked Method assert_equal :happy, @dog.wag # Normal Method end end
The nice thing about this technique is that after the test is over, the mocked out methods are returned to their normal state. Outside the test everything is back to normal.
NOTE: In previous versions of FlexMock, partial mocking was called “stubs”
and the flexstub
method was used to create the partial mocks.
Although partial mocks were often used as stubs, the terminology was not
quite correct. The current version of FlexMock
uses the flexmock
method to create both regular stubs and
partial stubs. A version of the flexstub
method is included
for backwards compatibility. See Martin Fowler’s article Mocks
Aren’t Stubs (www.martinfowler.com/articles/mocksArentStubs.html)
for a better understanding of the difference between mocks and stubs.
This partial mocking technique was inspired by the Stuba
library in the Mocha
project.
In the previous example we mocked out the bark
method of a Dog
object to avoid invoking the Woofer object. Perhaps a better technique
would be to mock the Woofer object directly. But Dog uses Woofer explicitly
so we cannot just pass in a mock object for Dog to use.
But wait, we can add mock behavior to any existing object, and classes are objects in Ruby. So why don’t we just mock out the Woofer class object to return mocks for us.
class TestDogBarking < Test::Unit::TestCase include FlexMock::TestCase # Setup the tests by mocking the +new+ method of # Woofer and return a mock woofer. def setup flexmock(Woofer).should_receive(:new). and_return(flexmock(:woof => :grrr)) @dog = Dog.new end def test_dog assert_equal :grrrr, @dog.bark # Calls woof on mock object # returned by Woofer.new end end
Sometimes returning a single mock object is not enough. Occasionally you want to mock every instance object created by a class. FlexMock makes this very easy.
class TestDogBarking < Test::Unit::TestCase include FlexMock::TestCase # Setup the tests by mocking Woofer to always # return partial mocks. def setup flexmock(Woofer).new_instances.should_receive(:woof => :grrr) end def test_dog assert_equal :grrrr, Dog.new.bark # All dog objects assert_equal :grrrr, Dog.new.bark # are mocked. end end
Note that FlexMock adds the mock 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 non-mocked version of the object.
Note that new_instances
will accept a block if you wish to
mock several methods at the same time. E.g.
flexmock(Woofer).new_instances do |m| m.should_receive(:woof).twice.and_return(:grrr) m.should_receive(:wag).at_least.once.and_return(:happy) end
Sometimes you want to setup a bunch of default expectations that are pretty
much for a number of different tests. Then in the individual tests, you
would like to override the default behavior on just that one method you are
testing at the moment. You can do that by using the
by_default
modifier.
In your test setup you might have:
def setup @mock_dog = flexmock("Fido") @mock_dog.should_receive(:tail => :a_tail, :bark => "woof").by_default end
The behaviors for :tail and :bark are good for most of the tests, but perhaps you wish to verify that :bark is called exactly once in a given test. Since :bark by default has no count expectations, you can override the default in the given test.
def test_something_where_bark_must_be_called_once @mock_dog.should_receive(:bark => "woof").once # At this point, the default for :bark is ignored, # and the "woof" value will be returned. # However, the default for :tail (which returns :a_tail) # is still active. end
By setting defaults, your individual tests don’t have to concern themselves with details of all the default setup. But the details of the overrides are right there in the body of the test.
The Law of Demeter says that you should only invoke methods on objects to which you have a direct connection, e.g. parameters, instance variables, and local variables. You can usually detect Law of Demeter violations by the excessive number of periods in an expression. For example:
car.chassis.axle.universal_joint.cog.turn
The Law of Demeter has a very big impact on mocking. If you need to mock the “turn” method on “cog”, you first have to mock chassis, axle, and universal_joint.
# Manually mocking a Law of Demeter violation cog = flexmock("cog") cog.should_receive(:turn).once.and_return(:ok) joint = flexmock("gear", :cog => cog) axle = flexmock("axle", :universal_joint => joint) chassis = flexmock("chassis", :axle => axle) car = flexmock("car", :chassis => chassis)
Yuck!
The best course of action is to avoid Law of Demeter violations. Then your mocking exploits will be very simple. However, sometimes you have to deal with code that already has a Demeter chain of method calls. So for those cases where you can’t avoid it, FlexMock will allow you to easily mock Demeter method chains.
Here’s an example of Demeter chain mocking:
# Demeter chain mocking using the short form. car = flexmock("car") car.should_receive( "chassis.axle.universal_joint.cog.turn" => :ok).once
You can also use the long form:
# Demeter chain mocking using the long form. car = flexmock("car") car.should_receive("chassis.axle.universal_joint.cog.turn").once. and_return(:ok)
That’s it. Anywhere FlexMock accepts a method name for mocking, you can use a demeter chain and FlexMock will attempt to do the right thing.
But beware, there are a few limitations.
The all the methods in the chain, except for the last one, will mocked to return a mock object. That mock object, in turn, will be mocked so as to respond to the next method in the chain, returning the following mock. And so on. If you try to manually mock out any of the chained methods, you could easily interfer with the mocking specified by the Demeter chain. FlexMock will attempt to catch problems when it can, but there are certainly scenarios where it cannot detect the problem beforehand.
require 'flexmock/test_unit' class TestSimple < Test::Unit::TestCase def test_simple_mock m = flexmock(:pi => 3.1416, :e => 2.71) assert_equal 3.1416, m.pi assert_equal 2.71, m.e end end
require 'flexmock/test_unit' class TestUndefined < Test::Unit::TestCase def test_undefined_values m = flexmock("mock") m.should_receive(:divide_by).with(0). and_return_undefined assert_equal FlexMock.undefined, m.divide_by(0) end end
Multiple calls to the query method will be allows, and calls may have any argument list. Each call to query will return the three element array [1, 2, 3]. The call to update must have a specific argument of 5.
require 'flexmock/test_unit' class TestDb < Test::Unit::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
(This and following examples assume that the ‘flexmock/test_unit’ file has been required.)
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_receive(:update).and_return(nil).ordered # test code here end
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(/^....$/).and_return(3.3). at_least.once.ordered(:queries) db.should_receive(:finish).once.ordered # test code here end
The record mode interface offers much the same features as the
should_receive
interface introduced so far, but it allows the
messages to be sent directly to a recording object rather than be specified
indirectly using a symbol.
def test_ordered_queries_in_record_mode db = flexmock('db') db.should_expect do |rec| rec.startup.once.ordered rec.query("CPWR") { 12.3 }.once.ordered(:queries) rec.query("MSFT") { 10.0 }.once.ordered(:queries) rec.query(/^....$/) { 3.3 }.at_least.once.ordered(:queries) rec.finish.once.ordered end # test code here using +db+. end
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.
Note: 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
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
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_receive(:an_important_message).and_return(1).once m.should_ignore_missing # test code here end
When should_ignore_missing
is enabled, ignored missing methods
will return an undefined object. Any operation on the undefined object
will return the undefined object.
The Portfolio class calculate the value of a set of stocks by talking to a quote service via a web service. Since we don’t want to use a real web service in our unit tests, we will mock the quote service.
def test_portfolio_value flexmock(QuoteService).new_instances do |m| m.should_receive(:quote).and_return(100) end port = Portfolio.new value = port.value # Portfolio calls QuoteService.quote assert_equal 100, value end
Copyright 2003, 2004, 2005, 2006, 2007 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.
Jim Weirich <jim@weirichhouse.org>
Ruby 1.8.7 or later (Use Flexmock-0.8.8 for Ruby version 1.8.6)
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.