# RSpec Mocks [![Build Status](https://secure.travis-ci.org/rspec/rspec-mocks.png?branch=master)](http://travis-ci.org/rspec/rspec-mocks) [![Code Climate](https://codeclimate.com/github/rspec/rspec-mocks.png)](https://codeclimate.com/github/rspec/rspec-mocks)

rspec-mocks is a test-double framework for rspec with support for method stubs,
fakes, and message expectations on generated test-doubles and real objects
alike.

## Install

    gem install rspec       # for rspec-core, rspec-expectations, rspec-mocks
    gem install rspec-mocks # for rspec-mocks only

## Test Doubles

A Test Double is an object that stands in for a real object in a test.
RSpec creates test doubles that support method stubs and message
expectations.

```ruby
book = double("book")
```

## Method Stubs

A method stub is an implementation that returns a pre-determined value.  Method
stubs can be declared on test doubles or real objects using the same syntax.
rspec-mocks supports 3 forms for declaring method stubs:

```ruby
book.stub(:title) { "The RSpec Book" }
book.stub(:title => "The RSpec Book")
book.stub(:title).and_return("The RSpec Book")
```

You can also use this shortcut, which creates a test double and declares a
method stub in one statement:

```ruby
book = double("book", :title => "The RSpec Book")
```

The first argument is a name, which is used for documentation and appears in
failure messages. If you don't care about the name, you can leave it out,
making the combined instantiation/stub declaration very terse:

```ruby
double(:foo => 'bar')
```

This is particularly nice when providing a list of test doubles to a method
that iterates through them:

```ruby
order.calculate_total_price(double(:price => 1.99),double(:price => 2.99))
```

## Consecutive return values

When a stub might be invoked more than once, you can provide additional
arguments to `and_return`.  The invocations cycle through the list. The last
value is returned for any subsequent invocations:

```ruby
die.stub(:roll).and_return(1,2,3)
die.roll # => 1
die.roll # => 2
die.roll # => 3
die.roll # => 3
die.roll # => 3
```

To return an array in a single invocation, declare an array:

```ruby
team.stub(:players).and_return([stub(:name => "David")])
```

## Message Expectations

A message expectation is an expectation that the test double will receive a
message some time before the example ends. If the message is received, the
expectation is satisfied. If not, the example fails.

```ruby
validator = double("validator")
validator.should_receive(:validate).with("02134")
zipcode = Zipcode.new("02134", validator)
zipcode.valid?
```

## Nomenclature

### Mock Objects and Test Stubs

The names Mock Object and Test Stub suggest specialized Test Doubles.  i.e.
a Test Stub is a Test Double that only supports method stubs, and a Mock
Object is a Test Double that supports message expectations and method
stubs.

There is a lot of overlapping nomenclature here, and there are many
variations of these patterns (fakes, spies, etc). Keep in mind that most of
the time we're talking about method-level concepts that are variations of
method stubs and message expectations, and we're applying to them to _one_
generic kind of object: a Test Double.

### Test-Specific Extension

a.k.a. Partial Stub/Mock, a Test-Specific Extension is an extension of a
real object in a system that is instrumented with test-double like
behaviour in the context of a test. This technique is very common in Ruby
because we often see class objects acting as global namespaces for methods.
For example, in Rails:

```ruby
person = double("person")
Person.stub(:find) { person }
```

In this case we're instrumenting Person to return the person object we've
defined whenever it receives the `find` message. We can also set a message
expectation so that the example fails if `find` is not called:

```ruby
person = double("person")
Person.should_receive(:find) { person }
```

We can do this with any object in a system because rspec-mocks adds the `stub`
and `should_receive` methods to every object, including class objects. When we
use either, RSpec replaces the method we're stubbing or mocking with its own
test-double-like method. At the end of the example, RSpec verifies any message
expectations, and then restores the original methods.

## Expecting Arguments

```ruby
double.should_receive(:msg).with(*args)
double.should_not_receive(:msg).with(*args)
```

You can set multiple expectations for the same message if you need to:

```ruby
double.should_receive(:msg).with("A", 1, 3)
double.should_receive(:msg).with("B", 2, 4)
```

## Argument Matchers

Arguments that are passed to `with` are compared with actual arguments
received using ==. In cases in which you want to specify things about the
arguments rather than the arguments themselves, you can use any of the
matchers that ship with rspec-expectations. They don't all make syntactic
sense (they were primarily designed for use with RSpec::Expectations), but
you are free to create your own custom RSpec::Matchers.

rspec-mocks also adds some keyword Symbols that you can use to
specify certain kinds of arguments:

```ruby
double.should_receive(:msg).with(no_args())
double.should_receive(:msg).with(any_args())
double.should_receive(:msg).with(1, kind_of(Numeric), "b") #2nd argument can be any kind of Numeric
double.should_receive(:msg).with(1, boolean(), "b") #2nd argument can be true or false
double.should_receive(:msg).with(1, /abc/, "b") #2nd argument can be any String matching the submitted Regexp
double.should_receive(:msg).with(1, anything(), "b") #2nd argument can be anything at all
double.should_receive(:msg).with(1, duck_type(:abs, :div), "b")
                    #2nd argument can be object that responds to #abs and #div
```

## Receive Counts

```ruby
double.should_receive(:msg).once
double.should_receive(:msg).twice
double.should_receive(:msg).exactly(n).times
double.should_receive(:msg).at_least(:once)
double.should_receive(:msg).at_least(:twice)
double.should_receive(:msg).at_least(n).times
double.should_receive(:msg).at_most(:once)
double.should_receive(:msg).at_most(:twice)
double.should_receive(:msg).at_most(n).times
double.should_receive(:msg).any_number_of_times
```

## Ordering

```ruby
double.should_receive(:msg).ordered
double.should_receive(:other_msg).ordered
  #This will fail if the messages are received out of order
```

This can include the same message with different arguments:

```ruby
double.should_receive(:msg).with("A", 1, 3).ordered
double.should_receive(:msg).with("B", 2, 4).ordered
```

## Setting Responses

Whether you are setting a message expectation or a method stub, you can
tell the object precisely how to respond. The most generic way is to pass
a block to `stub` or `should_receive`:

```ruby
double.should_receive(:msg) { value }
```

When the double receives the `msg` message, it evaluates the block and returns
the result.

```ruby
double.should_receive(:msg).and_return(value)
double.should_receive(:msg).exactly(3).times.and_return(value1, value2, value3)
  # returns value1 the first time, value2 the second, etc
double.should_receive(:msg).and_raise(error)
  #error can be an instantiated object or a class
  #if it is a class, it must be instantiable with no args
double.should_receive(:msg).and_throw(:msg)
double.should_receive(:msg).and_yield(values,to,yield)
double.should_receive(:msg).and_yield(values,to,yield).and_yield(some,other,values,this,time)
  # for methods that yield to a block multiple times
```

Any of these responses can be applied to a stub as well

```ruby
double.stub(:msg).and_return(value)
double.stub(:msg).and_return(value1, value2, value3)
double.stub(:msg).and_raise(error)
double.stub(:msg).and_throw(:msg)
double.stub(:msg).and_yield(values,to,yield)
double.stub(:msg).and_yield(values,to,yield).and_yield(some,other,values,this,time)
```

## Arbitrary Handling

Once in a while you'll find that the available expectations don't solve the
particular problem you are trying to solve. Imagine that you expect the message
to come with an Array argument that has a specific length, but you don't care
what is in it. You could do this:

```ruby
double.should_receive(:msg) do |arg|
  arg.size.should eq(7)
end
```

If the method being stubbed itself takes a block, and you need to yield to it
in some special way, you can use this:

```ruby
double.should_receive(:msg) do |&arg|
  begin
    arg.call
  ensure
    # cleanup
  end
end
```

## Delegating to the Original Implementation

When working with a partial mock object, you may occasionally
want to set a message expecation without interfering with how
the object responds to the message. You can use `and_call_original`
to achieve this:

```ruby
Person.should_receive(:find).and_call_original
Person.find # => executes the original find method and returns the result
```

## Combining Expectation Details

Combining the message name with specific arguments, receive counts and responses
you can get quite a bit of detail in your expectations:

```ruby
double.should_receive(:<<).with("illegal value").once.and_raise(ArgumentError)
```

While this is a good thing when you really need it, you probably don't really
need it! Take care to specify only the things that matter to the behavior of
your code.

## Stubbing and Hiding Constants

See the [mutating constants
README](https://github.com/rspec/rspec-mocks/blob/master/features/mutating_constants/README.md)
for info on this feature.

## Use `before(:each)`, not `before(:all)`

Stubs in `before(:all)` are not supported. The reason is that all stubs and mocks get cleared out after each example, so any stub that is set in `before(:all)` would work in the first example that happens to run in that group, but not for any others.

Instead of `before(:all)`, use `before(:each)`.

## Further Reading

There are many different viewpoints about the meaning of mocks and stubs. If
you are interested in learning more, here is some recommended reading:

* Mock Objects: http://www.mockobjects.com/
* Endo-Testing: http://www.mockobjects.com/files/endotesting.pdf
* Mock Roles, Not Objects: http://www.mockobjects.com/files/mockrolesnotobjects.pdf
* Test Double Patterns: http://xunitpatterns.com/Test%20Double%20Patterns.html
* Mocks aren't stubs: http://www.martinfowler.com/articles/mocksArentStubs.html

## Also see

* [http://github.com/rspec/rspec](http://github.com/rspec/rspec)
* [http://github.com/rspec/rspec-core](http://github.com/rspec/rspec-core)
* [http://github.com/rspec/rspec-expectations](http://github.com/rspec/rspec-expectations)