Class: Mocha::Mock

Inherits:
Object
  • Object
show all
Defined in:
lib/mocha/mock.rb

Overview

Traditional mock object.

#expects and #stubs return an Expectation which can be further modified by methods on Expectation.

#responds_like and #responds_like_instance_of both return a Mock, and can therefore, be chained to the original creation methods in API. They force the mock to indicate what it is supposed to be mocking, thus making it a safer verifying mock. They check that the underlying responder will actually respond to the methods being stubbed, throwing a NoMethodError upon invocation otherwise.

Stubs and expectations are basically the same thing. A stub is just an expectation of zero or more invocations. The #stubs method is syntactic sugar to make the intent of the test more explicit.

When a method is invoked on a mock object, the mock object searches through its expectations from newest to oldest to find one that matches the invocation. After the invocation, the matching expectation might stop matching further invocations. For example, an expects(:foo).once expectation only matches once and will be ignored on future invocations while an expects(:foo).at_least_once expectation will always be matched against invocations.

This scheme allows you to:

  • Set up default stubs in your the setup method of your test class and override some of those stubs in individual tests.

  • Set up different once expectations for the same method with different action per invocation. However, it’s better to use the Expectation#returns method with multiple arguments to do this, as described below.

However, there are some possible “gotchas” caused by this scheme:

  • if you create an expectation and then a stub for the same method, the stub will always override the expectation and the expectation will never be met.

  • if you create a stub and then an expectation for the same method, the expectation will match, and when it stops matching the stub will be used instead, possibly masking test failures.

  • if you create different expectations for the same method, they will be invoked in the opposite order than that in which they were specified, rather than the same order.

The best thing to do is not set up multiple expectations and stubs for the same method with exactly the same matchers. Instead, use the Expectation#returns method with multiple arguments to create multiple actions for a method. You can also chain multiple calls to Expectation#returns and Expectation#raises (along with syntactic sugar Expectation#then if desired).

If you want to specify more complex ordering or order invocations across different mock objects, use the Expectation#in_sequence method to explicitly define a total or partial ordering of invocations.

Examples:

object = mock()
object.stubs(:expected_method).returns(1, 2).then.raises(Exception)
object.expected_method # => 1
object.expected_method # => 2
object.expected_method # => raises exception of class Exception1

Instance Method Summary collapse

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(symbol, *arguments, &block) ⇒ Object

rubocop:disable Style/MethodMissingSuper



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# File 'lib/mocha/mock.rb', line 313

def method_missing(symbol, *arguments, &block)
  handle_method_call(symbol, arguments, block)
end

Instance Method Details

#expects(method_name) ⇒ Expectation #expects(expected_methods_vs_return_values) ⇒ Expectation Also known as: __expects__

Adds an expectation that the specified method must be called exactly once with any parameters.

Examples:

Expected method invoked once so no error raised

object = mock()
object.expects(:expected_method)
object.expected_method

Expected method not invoked so error raised

object = mock()
object.expects(:expected_method)
# error raised when test completes, because expected_method not called exactly once

Expected method invoked twice so error raised

object = mock()
object.expects(:expected_method)
object.expected_method
object.expected_method # => error raised when expected method invoked second time

Setup multiple expectations using expected_methods_vs_return_values.

object = mock()
object.expects(:expected_method_one => :result_one, :expected_method_two => :result_two)

# is exactly equivalent to

object = mock()
object.expects(:expected_method_one).returns(:result_one)
object.expects(:expected_method_two).returns(:result_two)

Overloads:

  • #expects(method_name) ⇒ Expectation

    Parameters:

    • method_name (Symbol, String) —

      name of expected method

  • #expects(expected_methods_vs_return_values) ⇒ Expectation

    Parameters:

    • expected_methods_vs_return_values (Hash) —

      expected method name symbols as keys and corresponding return values as values - these expectations are setup as if #expects were called multiple times.

Returns:



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# File 'lib/mocha/mock.rb', line 110

def expects(method_name_or_hash, backtrace = nil)
  expectation = nil
  iterator = ArgumentIterator.new(method_name_or_hash)
  iterator.each do |*args|
    method_name = args.shift
    ensure_method_not_already_defined(method_name)
    expectation = Expectation.new(self, method_name, backtrace)
    expectation.returns(args.shift) unless args.empty?
    @expectations.add(expectation)
  end
  expectation
end

#responds_like(responder) ⇒ Mock Also known as: quacks_like

Constrains the Mocha::Mock instance so that it can only expect or stub methods to which responder responds publicly. The constraint is only applied at method invocation time.

A NoMethodError will be raised if the responder does not publicly #respond_to? the invoked method (even if the method has been expected or stubbed).

The Mocha::Mock instance will delegate its #respond_to? method to the responder. However, the include_all parameter is not passed through, so only public methods on the responder will be considered.

Note that the methods on responder are never actually invoked.

Examples:

Normal mocking

sheep = mock('sheep')
sheep.expects(:chew)
sheep.expects(:foo)
sheep.respond_to?(:chew) # => true
sheep.respond_to?(:foo) # => true
sheep.chew
sheep.foo
# no error raised

Using #responds_like with an instance method

class Sheep
  def chew(grass); end
end

sheep = mock('sheep')
sheep.responds_like(Sheep.new)
sheep.expects(:chew)
sheep.expects(:foo)
sheep.respond_to?(:chew) # => true
sheep.respond_to?(:foo) # => false
sheep.chew
sheep.foo # => raises NoMethodError exception

Using #responds_like with a class method

class Sheep
  def self.number_of_legs; end
end

sheep_class = mock('sheep_class')
sheep_class.responds_like(Sheep)
sheep_class.stubs(:number_of_legs).returns(4)
sheep_class.expects(:foo)
sheep_class.respond_to?(:number_of_legs) # => true
sheep_class.respond_to?(:foo) # => false
sheep_class.number_of_legs # => 4
sheep_class.foo # => raises NoMethodError exception

Parameters:

  • responder (Object, #respond_to?) —

    an object used to determine whether Mocha::Mock instance should #respond_to? to an invocation.

Returns:

See Also:



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# File 'lib/mocha/mock.rb', line 235

def responds_like(responder)
  @responder = responder
  self
end

#responds_like_instance_of(responder_class) ⇒ Mock Also known as: quacks_like_instance_of

Constrains the Mocha::Mock instance so that it can only expect or stub methods to which an instance of the responder_class responds publicly. The constraint is only applied at method invocation time. Note that the responder instance is instantiated using Class#allocate.

A NoMethodError will be raised if the responder instance does not publicly #respond_to? the invoked method (even if the method has been expected or stubbed).

The Mocha::Mock instance will delegate its #respond_to? method to the responder instance. However, the include_all parameter is not passed through, so only public methods on the responder will be considered.

Note that the methods on the responder instance are never actually invoked.

Examples:

Using #responds_like_instance_of

class Sheep
  def initialize
    raise "some awkward code we don't want to call"
  end
  def chew(grass); end
end

sheep = mock('sheep')
sheep.responds_like_instance_of(Sheep)
sheep.expects(:chew)
sheep.expects(:foo)
sheep.respond_to?(:chew) # => true
sheep.respond_to?(:foo) # => false
sheep.chew
sheep.foo # => raises NoMethodError exception

Parameters:

  • responder_class (Class) —

    a class used to determine whether Mocha::Mock instance should #respond_to? to an invocation.

Returns:

See Also:



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# File 'lib/mocha/mock.rb', line 268

def responds_like_instance_of(responder_class)
  responds_like(responder_class.allocate)
end

#stubs(method_name) ⇒ Expectation #stubs(stubbed_methods_vs_return_values) ⇒ Expectation Also known as: __stubs__

Adds an expectation that the specified method may be called any number of times with any parameters.

Examples:

No error raised however many times stubbed method is invoked

object = mock()
object.stubs(:stubbed_method)
object.stubbed_method
object.stubbed_method
# no error raised

Setup multiple expectations using stubbed_methods_vs_return_values.

object = mock()
object.stubs(:stubbed_method_one => :result_one, :stubbed_method_two => :result_two)

# is exactly equivalent to

object = mock()
object.stubs(:stubbed_method_one).returns(:result_one)
object.stubs(:stubbed_method_two).returns(:result_two)

Overloads:

  • #stubs(method_name) ⇒ Expectation

    Parameters:

    • method_name (Symbol, String) —

      name of stubbed method

  • #stubs(stubbed_methods_vs_return_values) ⇒ Expectation

    Parameters:

    • stubbed_methods_vs_return_values (Hash) —

      stubbed method name symbols as keys and corresponding return values as values - these stubbed methods are setup as if #stubs were called multiple times.

Returns:



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# File 'lib/mocha/mock.rb', line 148

def stubs(method_name_or_hash, backtrace = nil)
  expectation = nil
  iterator = ArgumentIterator.new(method_name_or_hash)
  iterator.each do |*args|
    method_name = args.shift
    ensure_method_not_already_defined(method_name)
    expectation = Expectation.new(self, method_name, backtrace)
    expectation.at_least(0)
    expectation.returns(args.shift) unless args.empty?
    @expectations.add(expectation)
  end
  expectation
end

#unstub(*method_names) ⇒ Object

Removes the specified stubbed methods (added by calls to #expects or #stubs) and all expectations associated with them.

Examples:

Invoking an unstubbed method causes error to be raised

object = mock('mock')
object.stubs(:stubbed_method).returns(:result_one)
object.stubbed_method # => :result_one
object.unstub(:stubbed_method)
object.stubbed_method # => unexpected invocation: #<Mock:mock>.stubbed_method()

Unstubbing multiple methods.

multiplier.unstub(:double, :triple)

# exactly equivalent to

multiplier.unstub(:double)
multiplier.unstub(:triple)

Parameters:

  • method_names (Array<Symbol>) —

    names of methods to unstub.



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# File 'lib/mocha/mock.rb', line 180

def unstub(*method_names)
  method_names.each do |method_name|
    @expectations.remove_all_matching_method(method_name)
  end
end