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

RSpec::Expectations lets you express expected outcomes on an object in an
example.

```ruby
expect(account.balance).to eq(Money.new(37.42, :USD))
```

## Install

If you want to use rspec-expectations with rspec, just install the rspec gem
and RubyGems will also install rspec-expectations for you (along with
rspec-core and rspec-mocks):

    gem install rspec

Want to run against the `master` branch? You'll need to include the dependent
RSpec repos as well. Add the following to your `Gemfile`:

```ruby
%w[rspec-core rspec-expectations rspec-mocks rspec-support].each do |lib|
  gem lib, :git => "git://github.com/rspec/#{lib}.git", :branch => 'master'
end
```

If you want to use rspec-expectations with another tool, like Test::Unit,
Minitest, or Cucumber, you can install it directly:

    gem install rspec-expectations

## Contributing

Once you've set up the environment, you'll need to cd into the working
directory of whichever repo you want to work in. From there you can run the
specs and cucumber features, and make patches.

NOTE: You do not need to use rspec-dev to work on a specific RSpec repo. You
can treat each RSpec repo as an independent project.

- [Build details](BUILD_DETAIL.md)
- [Code of Conduct](CODE_OF_CONDUCT.md)
- [Detailed contributing guide](CONTRIBUTING.md)
- [Development setup guide](DEVELOPMENT.md)

## Basic usage

Here's an example using rspec-core:

```ruby
RSpec.describe Order do
  it "sums the prices of the items in its line items" do
    order = Order.new
    order.add_entry(LineItem.new(:item => Item.new(
      :price => Money.new(1.11, :USD)
    )))
    order.add_entry(LineItem.new(:item => Item.new(
      :price => Money.new(2.22, :USD),
      :quantity => 2
    )))
    expect(order.total).to eq(Money.new(5.55, :USD))
  end
end
```

The `describe` and `it` methods come from rspec-core.  The `Order`, `LineItem`, `Item` and `Money` classes would be from _your_ code. The last line of the example
expresses an expected outcome. If `order.total == Money.new(5.55, :USD)`, then
the example passes. If not, it fails with a message like:

    expected: #<Money @value=5.55 @currency=:USD>
         got: #<Money @value=1.11 @currency=:USD>

## Built-in matchers

### Equivalence

```ruby
expect(actual).to eq(expected)  # passes if actual == expected
expect(actual).to eql(expected) # passes if actual.eql?(expected)
expect(actual).not_to eql(not_expected) # passes if not(actual.eql?(expected))
```

Note: The new `expect` syntax no longer supports the `==` matcher.

### Identity

```ruby
expect(actual).to be(expected)    # passes if actual.equal?(expected)
expect(actual).to equal(expected) # passes if actual.equal?(expected)
```

### Comparisons

```ruby
expect(actual).to be >  expected
expect(actual).to be >= expected
expect(actual).to be <= expected
expect(actual).to be <  expected
expect(actual).to be_within(delta).of(expected)
```

### Regular expressions

```ruby
expect(actual).to match(/expression/)
```

Note: The new `expect` syntax no longer supports the `=~` matcher.

### Types/classes

```ruby
expect(actual).to be_an_instance_of(expected) # passes if actual.class == expected
expect(actual).to be_a(expected)              # passes if actual.kind_of?(expected)
expect(actual).to be_an(expected)             # an alias for be_a
expect(actual).to be_a_kind_of(expected)      # another alias
```

### Truthiness

```ruby
expect(actual).to be_truthy   # passes if actual is truthy (not nil or false)
expect(actual).to be true     # passes if actual == true
expect(actual).to be_falsy    # passes if actual is falsy (nil or false)
expect(actual).to be false    # passes if actual == false
expect(actual).to be_nil      # passes if actual is nil
expect(actual).to_not be_nil  # passes if actual is not nil
```

### Expecting errors

```ruby
expect { ... }.to raise_error
expect { ... }.to raise_error(ErrorClass)
expect { ... }.to raise_error("message")
expect { ... }.to raise_error(ErrorClass, "message")
```

### Expecting throws

```ruby
expect { ... }.to throw_symbol
expect { ... }.to throw_symbol(:symbol)
expect { ... }.to throw_symbol(:symbol, 'value')
```

### Yielding

```ruby
expect { |b| 5.tap(&b) }.to yield_control # passes regardless of yielded args

expect { |b| yield_if_true(true, &b) }.to yield_with_no_args # passes only if no args are yielded

expect { |b| 5.tap(&b) }.to yield_with_args(5)
expect { |b| 5.tap(&b) }.to yield_with_args(Integer)
expect { |b| "a string".tap(&b) }.to yield_with_args(/str/)

expect { |b| [1, 2, 3].each(&b) }.to yield_successive_args(1, 2, 3)
expect { |b| { :a => 1, :b => 2 }.each(&b) }.to yield_successive_args([:a, 1], [:b, 2])
```

### Predicate matchers

```ruby
expect(actual).to be_xxx         # passes if actual.xxx?
expect(actual).to have_xxx(:arg) # passes if actual.has_xxx?(:arg)
```

### Ranges (Ruby >= 1.9 only)

```ruby
expect(1..10).to cover(3)
```

### Collection membership

```ruby
expect(actual).to include(expected)
expect(actual).to start_with(expected)
expect(actual).to end_with(expected)

expect(actual).to contain_exactly(individual, items)
# ...which is the same as:
expect(actual).to match_array(expected_array)
```

#### Examples

```ruby
expect([1, 2, 3]).to include(1)
expect([1, 2, 3]).to include(1, 2)
expect([1, 2, 3]).to start_with(1)
expect([1, 2, 3]).to start_with(1, 2)
expect([1, 2, 3]).to end_with(3)
expect([1, 2, 3]).to end_with(2, 3)
expect({:a => 'b'}).to include(:a => 'b')
expect("this string").to include("is str")
expect("this string").to start_with("this")
expect("this string").to end_with("ring")
expect([1, 2, 3]).to contain_exactly(2, 3, 1)
expect([1, 2, 3]).to match_array([3, 2, 1])
```

## `should` syntax

In addition to the `expect` syntax, rspec-expectations continues to support the
`should` syntax:

```ruby
actual.should eq expected
actual.should be > 3
[1, 2, 3].should_not include 4
```

See [detailed information on the `should` syntax and its usage.](https://github.com/rspec/rspec-expectations/blob/master/Should.md)

## Compound Matcher Expressions

You can also create compound matcher expressions using `and` or `or`:

``` ruby
expect(alphabet).to start_with("a").and end_with("z")
expect(stoplight.color).to eq("red").or eq("green").or eq("yellow")
```

## Composing Matchers

Many of the built-in matchers are designed to take matchers as
arguments, to allow you to flexibly specify only the essential
aspects of an object or data structure. In addition, all of the
built-in matchers have one or more aliases that provide better
phrasing for when they are used as arguments to another matcher.

### Examples

```ruby
expect { k += 1.05 }.to change { k }.by( a_value_within(0.1).of(1.0) )

expect { s = "barn" }.to change { s }
  .from( a_string_matching(/foo/) )
  .to( a_string_matching(/bar/) )

expect(["barn", 2.45]).to contain_exactly(
  a_value_within(0.1).of(2.5),
  a_string_starting_with("bar")
)

expect(["barn", "food", 2.45]).to end_with(
  a_string_matching("foo"),
  a_value > 2
)

expect(["barn", 2.45]).to include( a_string_starting_with("bar") )

expect(:a => "food", :b => "good").to include(:a => a_string_matching(/foo/))

hash = {
  :a => {
    :b => ["foo", 5],
    :c => { :d => 2.05 }
  }
}

expect(hash).to match(
  :a => {
    :b => a_collection_containing_exactly(
      a_string_starting_with("f"),
      an_instance_of(Integer)
    ),
    :c => { :d => (a_value < 3) }
  }
)

expect { |probe|
  [1, 2, 3].each(&probe)
}.to yield_successive_args( a_value < 2, 2, a_value > 2 )
```

## Usage outside rspec-core

You always need to load `rspec/expectations` even if you only want to use one part of the library:

```ruby
require 'rspec/expectations'
```

Then simply include `RSpec::Matchers` in any class:

```ruby
class MyClass
  include RSpec::Matchers

  def do_something(arg)
    expect(arg).to be > 0
    # do other stuff
  end
end
```

## Also see

* [https://github.com/rspec/rspec](https://github.com/rspec/rspec)
* [https://github.com/rspec/rspec-core](https://github.com/rspec/rspec-core)
* [https://github.com/rspec/rspec-mocks](https://github.com/rspec/rspec-mocks)
* [https://github.com/rspec/rspec-rails](https://github.com/rspec/rspec-rails)
