`RSpec` Expectations ¶ ↑

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

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 main branch? You’ll need to include the dependent RSpec repos as well. Add the following to your Gemfile:

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

Basic usage¶ ↑

Here’s an example using rspec-core:

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¶ ↑

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¶ ↑

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

Comparisons¶ ↑

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¶ ↑

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

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

Types/classes¶ ↑

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¶ ↑

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¶ ↑

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

Expecting throws¶ ↑

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

Yielding¶ ↑

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¶ ↑

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)¶ ↑

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

Collection membership¶ ↑

# exact order, entire collection
expect(actual).to eq(expected)

# exact order, partial collection (based on an exact position)
expect(actual).to start_with(expected)
expect(actual).to end_with(expected)

# any order, entire collection
expect(actual).to match_array(expected)

# You can also express this by passing the expected elements
# as individual arguments
expect(actual).to contain_exactly(expected_element1, expected_element2)

 # any order, partial collection
expect(actual).to include(expected)

Examples¶ ↑

expect([1, 2, 3]).to eq([1, 2, 3])            # Order dependent equality check
expect([1, 2, 3]).to include(1)               # Exact ordering, partial collection matches
expect([1, 2, 3]).to include(2, 3)            #
expect([1, 2, 3]).to start_with(1)            # As above, but from the start of the collection
expect([1, 2, 3]).to start_with(1, 2)         #
expect([1, 2, 3]).to end_with(3)              # As above but from the end of the collection
expect([1, 2, 3]).to end_with(2, 3)           #
expect({:a => 'b'}).to include(:a => 'b')     # Matching within hashes
expect("this string").to include("is str")    # Matching within strings
expect("this string").to start_with("this")   #
expect("this string").to end_with("ring")     #
expect([1, 2, 3]).to contain_exactly(2, 3, 1) # Order independent matches
expect([1, 2, 3]).to match_array([3, 2, 1])   #

# Order dependent compound matchers
expect(
  [{:a => 'hash'},{:a => 'another'}]
).to match([a_hash_including(:a => 'hash'), a_hash_including(:a => 'another')])

`should` syntax¶ ↑

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

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/main/Should.md]

Compound Matcher Expressions¶ ↑

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

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¶ ↑

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:

require 'rspec/expectations'

Then simply include RSpec::Matchers in any class:

class MyClass
  include RSpec::Matchers

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

RSpec Expectations ¶ ↑

Install¶ ↑

Contributing¶ ↑

Basic usage¶ ↑

Built-in matchers¶ ↑

Equivalence¶ ↑

Identity¶ ↑

Comparisons¶ ↑

Regular expressions¶ ↑

Types/classes¶ ↑

Truthiness¶ ↑

Expecting errors¶ ↑

Expecting throws¶ ↑

Yielding¶ ↑

Predicate matchers¶ ↑

Ranges (Ruby >= 1.9 only)¶ ↑

Collection membership¶ ↑

Examples¶ ↑

should syntax¶ ↑

Compound Matcher Expressions¶ ↑

Composing Matchers¶ ↑

Examples¶ ↑

Usage outside rspec-core¶ ↑

Also see¶ ↑

`RSpec` Expectations ¶ ↑

`should` syntax¶ ↑