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RSpec Expectations

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

expect(account.balance).to eq(, :USD))


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 => "{lib}.git", :branch => 'main'

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

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.add_entry( =>
:price =>, :USD)
order.add_entry( =>
:price =>, :USD),
:quantity => 2
expect( eq(, :USD))

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 ==, :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


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.


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


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.


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


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')


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
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)


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
[{: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.

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.


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(

expect(["barn", "food", 2.45]).to end_with(
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(
: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

Also see