Module: RSpec::Matchers

Extended by:
DSL
Included in:
DSL::Matcher
Defined in:
lib/rspec/matchers.rb,
lib/rspec/matchers/dsl.rb,
lib/rspec/matchers/built_in.rb,
lib/rspec/matchers/composable.rb,
lib/rspec/matchers/built_in/be.rb,
lib/rspec/matchers/built_in/eq.rb,
lib/rspec/matchers/built_in/all.rb,
lib/rspec/matchers/built_in/eql.rb,
lib/rspec/matchers/built_in/has.rb,
lib/rspec/matchers/fail_matchers.rb,
lib/rspec/matchers/built_in/cover.rb,
lib/rspec/matchers/built_in/equal.rb,
lib/rspec/matchers/built_in/exist.rb,
lib/rspec/matchers/built_in/match.rb,
lib/rspec/matchers/built_in/yield.rb,
lib/rspec/matchers/aliased_matcher.rb,
lib/rspec/matchers/built_in/change.rb,
lib/rspec/matchers/built_in/output.rb,
lib/rspec/matchers/built_in/include.rb,
lib/rspec/matchers/built_in/satisfy.rb,
lib/rspec/matchers/english_phrasing.rb,
lib/rspec/matchers/matcher_protocol.rb,
lib/rspec/matchers/built_in/compound.rb,
lib/rspec/matchers/matcher_delegator.rb,
lib/rspec/matchers/built_in/be_within.rb,
lib/rspec/matchers/built_in/operators.rb,
lib/rspec/matchers/built_in/be_between.rb,
lib/rspec/matchers/built_in/be_kind_of.rb,
lib/rspec/matchers/built_in/respond_to.rb,
lib/rspec/matchers/built_in/raise_error.rb,
lib/rspec/matchers/built_in/base_matcher.rb,
lib/rspec/matchers/built_in/throw_symbol.rb,
lib/rspec/matchers/generated_descriptions.rb,
lib/rspec/matchers/built_in/be_instance_of.rb,
lib/rspec/matchers/built_in/contain_exactly.rb,
lib/rspec/matchers/built_in/have_attributes.rb,
lib/rspec/matchers/built_in/start_or_end_with.rb,
lib/rspec/matchers/expecteds_for_multiple_diffs.rb

Overview

RSpec::Matchers provides a number of useful matchers we use to define expectations. Any object that implements the matcher protocol can be used as a matcher.

Predicates

In addition to matchers that are defined explicitly, RSpec will create custom matchers on the fly for any arbitrary predicate, giving your specs a much more natural language feel.

A Ruby predicate is a method that ends with a "?" and returns true or false. Common examples are empty?, nil?, and instance_of?.

All you need to do is write expect(..).to be_ followed by the predicate without the question mark, and RSpec will figure it out from there. For example:

expect([]).to be_empty     # => [].empty?() | passes
expect([]).not_to be_empty # => [].empty?() | fails

In addtion to prefixing the predicate matchers with "be_", you can also use "be_a_" and "be_an_", making your specs read much more naturally:

expect("a string").to be_an_instance_of(String) # =>"a string".instance_of?(String) # passes

expect(3).to be_a_kind_of(Integer)          # => 3.kind_of?(Numeric)     | passes
expect(3).to be_a_kind_of(Numeric)          # => 3.kind_of?(Numeric)     | passes
expect(3).to be_an_instance_of(Integer)     # => 3.instance_of?(Integer) | passes
expect(3).not_to be_an_instance_of(Numeric) # => 3.instance_of?(Numeric) | fails

RSpec will also create custom matchers for predicates like has_key?. To use this feature, just state that the object should have_key(:key) and RSpec will call has_key?(:key) on the target. For example:

expect(:a => "A").to have_key(:a)
expect(:a => "A").to have_key(:b) # fails

You can use this feature to invoke any predicate that begins with "has_", whether it is part of the Ruby libraries (like Hash#has_key?) or a method you wrote on your own class.

Note that RSpec does not provide composable aliases for these dynamic predicate matchers. You can easily define your own aliases, though:

RSpec::Matchers.alias_matcher :a_user_who_is_an_admin, :be_an_admin
expect(user_list).to include(a_user_who_is_an_admin)

Alias Matchers

With Matchers.alias_matcher, you can easily create an alternate name for a given matcher.

The description will also change according to the new name:

RSpec::Matchers.alias_matcher :a_list_that_sums_to, :sum_to
sum_to(3).description # => "sum to 3"
a_list_that_sums_to(3).description # => "a list that sums to 3"

or you can specify a custom description like this:

RSpec::Matchers.alias_matcher :a_list_sorted_by, :be_sorted_by do |description|
  description.sub("be sorted by", "a list sorted by")
end

be_sorted_by(:age).description # => "be sorted by age"
a_list_sorted_by(:age).description # => "a list sorted by age"

Custom Matchers

When you find that none of the stock matchers provide a natural feeling expectation, you can very easily write your own using RSpec's matcher DSL or writing one from scratch.

Matcher DSL

Imagine that you are writing a game in which players can be in various zones on a virtual board. To specify that bob should be in zone 4, you could say:

expect(bob.current_zone).to eql(Zone.new("4"))

But you might find it more expressive to say:

expect(bob).to be_in_zone("4")

and/or

expect(bob).not_to be_in_zone("3")

You can create such a matcher like so:

RSpec::Matchers.define :be_in_zone do |zone|
  match do |player|
    player.in_zone?(zone)
  end
end

This will generate a be_in_zone method that returns a matcher with logical default messages for failures. You can override the failure messages and the generated description as follows:

RSpec::Matchers.define :be_in_zone do |zone|
  match do |player|
    player.in_zone?(zone)
  end

  failure_message do |player|
    # generate and return the appropriate string.
  end

  failure_message_when_negated do |player|
    # generate and return the appropriate string.
  end

  description do
    # generate and return the appropriate string.
  end
end

Each of the message-generation methods has access to the block arguments passed to the create method (in this case, zone). The failure message methods (failure_message and failure_message_when_negated) are passed the actual value (the receiver of expect(..) or expect(..).not_to).

Custom Matcher from scratch

You could also write a custom matcher from scratch, as follows:

class BeInZone
  def initialize(expected)
    @expected = expected
  end

  def matches?(target)
    @target = target
    @target.current_zone.eql?(Zone.new(@expected))
  end

  def failure_message
    "expected #{@target.inspect} to be in Zone #{@expected}"
  end

  def failure_message_when_negated
    "expected #{@target.inspect} not to be in Zone #{@expected}"
  end
end

... and a method like this:

def be_in_zone(expected)
  BeInZone.new(expected)
end

And then expose the method to your specs. This is normally done by including the method and the class in a module, which is then included in your spec:

module CustomGameMatchers
  class BeInZone
    # ...
  end

  def be_in_zone(expected)
    # ...
  end
end

describe "Player behaviour" do
  include CustomGameMatchers
  # ...
end

or you can include in globally in a spec_helper.rb file required from your spec file(s):

RSpec::configure do |config|
  config.include(CustomGameMatchers)
end

Making custom matchers composable

RSpec's built-in matchers are designed to be composed, in expressions like:

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

Custom matchers can easily participate in composed matcher expressions like these. Include Composable in your custom matcher to make it support being composed (matchers defined using the DSL have this included automatically). Within your matcher's matches? method (or the match block, if using the DSL), use values_match?(expected, actual) rather than expected == actual. Under the covers, values_match? is able to match arbitrary nested data structures containing a mix of both matchers and non-matcher objects. It uses === and == to perform the matching, considering the values to match if either returns true. The Composable mixin also provides some helper methods for surfacing the matcher descriptions within your matcher's description or failure messages.

RSpec's built-in matchers each have a number of aliases that rephrase the matcher from a verb phrase (such as be_within) to a noun phrase (such as a_value_within), which reads better when the matcher is passed as an argument in a composed matcher expressions, and also uses the noun-phrase wording in the matcher's description, for readable failure messages. You can alias your custom matchers in similar fashion using Matchers.alias_matcher.

Negated Matchers

Sometimes if you want to test for the opposite using a more descriptive name instead of using not_to, you can use Matchers.define_negated_matcher:

RSpec::Matchers.define_negated_matcher :exclude, :include
include(1, 2).description # => "include 1 and 2"
exclude(1, 2).description # => "exclude 1 and 2"

While the most obvious negated form may be to add a not_ prefix, the failure messages you get with that form can be confusing (e.g. "expected [actual] to not [verb], but did not"). We've found it works best to find a more positive name for the negated form, such as avoid_changing rather than not_change.

Defined Under Namespace

Modules: BuiltIn, Composable, DSL, EnglishPhrasing, FailMatchers Classes: AliasedMatcher, ExpectedsForMultipleDiffs, MatcherProtocol

Class Method Summary collapse

Instance Method Summary collapse

Methods included from DSL

alias_matcher, define, define_negated_matcher

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(method, *args, &block) ⇒ Object (private)



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# File 'lib/rspec/matchers.rb', line 947

def method_missing(method, *args, &block)
  case method.to_s
  when BE_PREDICATE_REGEX
    BuiltIn::BePredicate.new(method, *args, &block)
  when HAS_REGEX
    BuiltIn::Has.new(method, *args, &block)
  else
    super
  end
end

Class Method Details

.alias_matcher(new_name, old_name, options = {}, &description_override) ⇒ Object



# File 'lib/rspec/matchers.rb', line 244


.clear_generated_descriptionObject

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Used by rspec-core to clear the state used to generate descriptions after an example.



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# File 'lib/rspec/matchers/generated_descriptions.rb', line 11

def self.clear_generated_description
  self.last_matcher = nil
  self.last_expectation_handler = nil
end

.configurationRSpec::Expectations::Configuration

Delegates to Expectations.configuration. This is here because rspec-core's expect_with option looks for a configuration method on the mixin (RSpec::Matchers) to yield to a block.

Returns:



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# File 'lib/rspec/matchers.rb', line 937

def self.configuration
  Expectations.configuration
end

.define(name, &declarations) ⇒ Object



# File 'lib/rspec/matchers.rb', line 247


.define_negated_matcher(negated_name, base_name, &description_override) ⇒ Object



# File 'lib/rspec/matchers.rb', line 250


.generated_descriptionObject

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Generates an an example description based on the last expectation. Used by rspec-core's one-liner syntax.



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# File 'lib/rspec/matchers/generated_descriptions.rb', line 19

def self.generated_description
  return nil if last_expectation_handler.nil?
  "#{last_expectation_handler.verb} #{last_description}"
end

Instance Method Details

#aggregate_failures(label = nil, metadata = {}) { ... } ⇒ Object

Note:

The implementation of this feature uses a thread-local variable, which means that if you have an expectation failure in another thread, it'll abort like normal.

Allows multiple expectations in the provided block to fail, and then aggregates them into a single exception, rather than aborting on the first expectation failure like normal. This allows you to see all failures from an entire set of expectations without splitting each off into its own example (which may slow things down if the example setup is expensive).

Examples:

aggregate_failures("verifying response") do
  expect(response.status).to eq(200)
  expect(response.headers).to include("Content-Type" => "text/plain")
  expect(response.body).to include("Success")
end

Parameters:

  • label (String) (defaults to: nil)

    label for this aggregation block, which will be included in the aggregated exception message.

  • metadata (Hash) (defaults to: {})

    additional metadata about this failure aggregation block. If multiple expectations fail, it will be exposed from the Expectations::MultipleExpectationsNotMetError exception. Mostly intended for internal RSpec use but you can use it as well.

Yields:

  • Block containing as many expectation as you want. The block is simply yielded to, so you can trust that anything that works outside the block should work within it.

Raises:



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# File 'lib/rspec/matchers.rb', line 295

def aggregate_failures(label=nil, ={}, &block)
  Expectations::FailureAggregator.new(label, ).aggregate(&block)
end

#all(expected) ⇒ Object

Note:

The negative form not_to all is not supported. Instead use not_to include or pass a negative form of a matcher as the argument (e.g. all exclude(:foo)).

Note:

You can also use this with compound matchers as well.

Passes if the provided matcher passes when checked against all elements of the collection.

Examples:

expect([1, 3, 5]).to all be_odd
expect([1, 3, 6]).to all be_odd # fails
expect([1, 3, 5]).to all( be_odd.and be_an(Integer) )


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# File 'lib/rspec/matchers.rb', line 653

def all(expected)
  BuiltIn::All.new(expected)
end

#be(*args) ⇒ Object

Given true, false, or nil, will pass if actual value is true, false or nil (respectively). Given no args means the caller should satisfy an if condition (to be or not to be).

Predicates are any Ruby method that ends in a "?" and returns true or false. Given be_ followed by arbitrary_predicate (without the "?"), RSpec will match convert that into a query against the target object.

The arbitrary_predicate feature will handle any predicate prefixed with "be_an_" (e.g. be_an_instance_of), "be_a_" (e.g. be_a_kind_of) or "be_" (e.g. be_empty), letting you choose the prefix that best suits the predicate.

Examples:

expect(actual).to     be_truthy
expect(actual).to     be_falsey
expect(actual).to     be_nil
expect(actual).to     be_[arbitrary_predicate](*args)
expect(actual).not_to be_nil
expect(actual).not_to be_[arbitrary_predicate](*args)


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# File 'lib/rspec/matchers.rb', line 343

def be(*args)
  args.empty? ? Matchers::BuiltIn::Be.new : equal(*args)
end

#be_a(klass) ⇒ Object Also known as: be_an

passes if target.kind_of?(klass)



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# File 'lib/rspec/matchers.rb', line 349

def be_a(klass)
  be_a_kind_of(klass)
end

#be_a_kind_of(expected) ⇒ Object Also known as: be_kind_of

Passes if actual.kind_of?(expected)

Examples:

expect(5).to     be_a_kind_of(Integer)
expect(5).to     be_a_kind_of(Numeric)
expect(5).not_to be_a_kind_of(Float)


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# File 'lib/rspec/matchers.rb', line 372

def be_a_kind_of(expected)
  BuiltIn::BeAKindOf.new(expected)
end

#be_an_instance_of(expected) ⇒ Object Also known as: be_instance_of

Passes if actual.instance_of?(expected)

Examples:

expect(5).to     be_an_instance_of(Integer)
expect(5).not_to be_an_instance_of(Numeric)
expect(5).not_to be_an_instance_of(Float)


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# File 'lib/rspec/matchers.rb', line 360

def be_an_instance_of(expected)
  BuiltIn::BeAnInstanceOf.new(expected)
end

#be_between(min, max) ⇒ Object

Passes if actual.between?(min, max). Works with any Comparable object, including String, Symbol, Time, or Numeric (Fixnum, Bignum, Integer, Float, Complex, and Rational).

By default, be_between is inclusive (i.e. passes when given either the max or min value), but you can make it exclusive by chaining that off the matcher.

Examples:

expect(5).to      be_between(1, 10)
expect(11).not_to be_between(1, 10)
expect(10).not_to be_between(1, 10).exclusive


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# File 'lib/rspec/matchers.rb', line 389

def be_between(min, max)
  BuiltIn::BeBetween.new(min, max)
end

#be_falseyObject

Passes if actual is falsey (false or nil)



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# File 'lib/rspec/matchers.rb', line 310

def be_falsey
  BuiltIn::BeFalsey.new
end

#be_nilObject

Passes if actual is nil



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# File 'lib/rspec/matchers.rb', line 318

def be_nil
  BuiltIn::BeNil.new
end

#be_truthyObject

Passes if actual is truthy (anything but false or nil)



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# File 'lib/rspec/matchers.rb', line 304

def be_truthy
  BuiltIn::BeTruthy.new
end

#be_within(delta) ⇒ Object

Passes if actual == expected +/- delta

Examples:

expect(result).to     be_within(0.5).of(3.0)
expect(result).not_to be_within(0.5).of(3.0)


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# File 'lib/rspec/matchers.rb', line 399

def be_within(delta)
  BuiltIn::BeWithin.new(delta)
end

#change(receiver = nil, message = nil, &block) ⇒ Object

Applied to a proc, specifies that its execution will cause some value to change.

You can either pass receiver and message, or a block, but not both.

When passing a block, it must use the { ... } format, not do/end, as { ... } binds to the change method, whereas do/end would errantly bind to the expect(..).to or expect(...).not_to method.

You can chain any of the following off of the end to specify details about the change:

  • from
  • to

or any one of:

  • by
  • by_at_least
  • by_at_most

== Notes

Evaluates receiver.message or block before and after it evaluates the block passed to expect.

expect( ... ).not_to change supports the form that specifies from (which specifies what you expect the starting, unchanged value to be) but does not support forms with subsequent calls to by, by_at_least, by_at_most or to.

Examples:

expect {
  team.add_player(player)
}.to change(roster, :count)

expect {
  team.add_player(player)
}.to change(roster, :count).by(1)

expect {
  team.add_player(player)
}.to change(roster, :count).by_at_least(1)

expect {
  team.add_player(player)
}.to change(roster, :count).by_at_most(1)

string = "string"
expect {
  string.reverse!
}.to change { string }.from("string").to("gnirts")

string = "string"
expect {
  string
}.not_to change { string }.from("string")

expect {
  person.happy_birthday
}.to change(person, :birthday).from(32).to(33)

expect {
  employee.develop_great_new_social_networking_app
}.to change(employee, :title).from("Mail Clerk").to("CEO")

expect {
  doctor.leave_office
}.to change(doctor, :sign).from(/is in/).to(/is out/)

user = User.new(:type => "admin")
expect {
  user.symbolize_type
}.to change(user, :type).from(String).to(Symbol)

Parameters:

  • receiver (Object) (defaults to: nil)
  • message (Symbol) (defaults to: nil)

    the message to send the receiver



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# File 'lib/rspec/matchers.rb', line 483

def change(receiver=nil, message=nil, &block)
  BuiltIn::Change.new(receiver, message, &block)
end

#contain_exactly(*items) ⇒ Object

Note:

This is also available using the =~ operator with should, but =~ is not supported with expect.

Passes if actual contains all of the expected regardless of order. This works for collections. Pass in multiple args and it will only pass if all args are found in collection.

Examples:

expect([1, 2, 3]).to contain_exactly(1, 2, 3)
expect([1, 2, 3]).to contain_exactly(1, 3, 2)

See Also:



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# File 'lib/rspec/matchers.rb', line 501

def contain_exactly(*items)
  BuiltIn::ContainExactly.new(items)
end

#cover(*values) ⇒ Object

Passes if actual covers expected. This works for Ranges. You can also pass in multiple args and it will only pass if all args are found in Range.

Warning:: Ruby >= 1.9 only

Examples:

expect(1..10).to     cover(5)
expect(1..10).to     cover(4, 6)
expect(1..10).to     cover(4, 6, 11) # fails
expect(1..10).not_to cover(11)
expect(1..10).not_to cover(5)        # fails


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# File 'lib/rspec/matchers.rb', line 519

def cover(*values)
  BuiltIn::Cover.new(*values)
end

#end_with(*expected) ⇒ Object

Matches if the actual value ends with the expected value(s). In the case of a string, matches against the last expected.length characters of the actual string. In the case of an array, matches against the last expected.length elements of the actual array.

Examples:

expect("this string").to   end_with "string"
expect([0, 1, 2, 3, 4]).to end_with 4
expect([0, 2, 3, 4, 4]).to end_with 3, 4


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# File 'lib/rspec/matchers.rb', line 534

def end_with(*expected)
  BuiltIn::EndWith.new(*expected)
end

#eq(expected) ⇒ Object

Passes if actual == expected.

See http://www.ruby-doc.org/core/classes/Object.html#M001057 for more information about equality in Ruby.

Examples:

expect(5).to     eq(5)
expect(5).not_to eq(3)


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# File 'lib/rspec/matchers.rb', line 549

def eq(expected)
  BuiltIn::Eq.new(expected)
end

#eql(expected) ⇒ Object

Passes if actual.eql?(expected)

See http://www.ruby-doc.org/core/classes/Object.html#M001057 for more information about equality in Ruby.

Examples:

expect(5).to     eql(5)
expect(5).not_to eql(3)


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# File 'lib/rspec/matchers.rb', line 563

def eql(expected)
  BuiltIn::Eql.new(expected)
end

#equal(expected) ⇒ Object

Passes if actual.equal?(expected) (object identity).

See http://www.ruby-doc.org/core/classes/Object.html#M001057 for more information about equality in Ruby.

Examples:

expect(5).to       equal(5)   # Integers are equal
expect("5").not_to equal("5") # Strings that look the same are not the same object


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# File 'lib/rspec/matchers.rb', line 577

def equal(expected)
  BuiltIn::Equal.new(expected)
end

#exist(*args) ⇒ Object

Passes if actual.exist? or actual.exists?

Examples:

expect(File).to exist("path/to/file")


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# File 'lib/rspec/matchers.rb', line 587

def exist(*args)
  BuiltIn::Exist.new(*args)
end

#expectExpectationTarget

Supports expect(actual).to matcher syntax by wrapping actual in an ExpectationTarget.

Examples:

expect(actual).to eq(expected)
expect(actual).not_to eq(expected)

Returns:

  • (ExpectationTarget)

See Also:

  • ExpectationTarget#to
  • ExpectationTarget#not_to


# File 'lib/rspec/matchers.rb', line 253


#have_attributes(expected) ⇒ Object

Note:

It will fail if actual doesn't respond to any of the expected attributes.

Passes if actual's attribute values match the expected attributes hash. This works no matter how you define your attribute readers.

Examples:

Person = Struct.new(:name, :age)
person = Person.new("Bob", 32)

expect(person).to have_attributes(:name => "Bob", :age => 32)
expect(person).to have_attributes(:name => a_string_starting_with("B"), :age => (a_value > 30) )
expect(person).to have_attributes(:color => "red")


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# File 'lib/rspec/matchers.rb', line 607

def have_attributes(expected)
  BuiltIn::HaveAttributes.new(expected)
end

#include(*expected) ⇒ Object

Passes if actual includes expected. This works for collections and Strings. You can also pass in multiple args and it will only pass if all args are found in collection.

Examples:

expect([1,2,3]).to      include(3)
expect([1,2,3]).to      include(2,3)
expect([1,2,3]).to      include(2,3,4) # fails
expect([1,2,3]).not_to  include(4)
expect("spread").to     include("read")
expect("spread").not_to include("red")
expect(:a => 1, :b => 2).to include(:a)
expect(:a => 1, :b => 2).to include(:a, :b)
expect(:a => 1, :b => 2).to include(:a => 1)
expect(:a => 1, :b => 2).to include(:b => 2, :a => 1)
expect(:a => 1, :b => 2).to include(:c) # fails
expect(:a => 1, :b => 2).not_to include(:a => 2)


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# File 'lib/rspec/matchers.rb', line 630

def include(*expected)
  BuiltIn::Include.new(*expected)
end

#match(expected) ⇒ Object

Note:

The match_regex alias is deprecated and is not recommended for use. It was added in 2.12.1 to facilitate its use from within custom matchers (due to how the custom matcher DSL was evaluated in 2.x, match could not be used there), but is no longer needed in 3.x.

Given a Regexp or String, passes if actual.match(pattern) Given an arbitrary nested data structure (e.g. arrays and hashes), matches if expected === actual || actual == expected for each pair of elements.

Examples:

expect(email).to match(/^([^\s]+)((?:[-a-z0-9]+\.)+[a-z]{2,})$/i)
expect(email).to match("@example.com")
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) }
  }
)


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# File 'lib/rspec/matchers.rb', line 688

def match(expected)
  BuiltIn::Match.new(expected)
end

#match_array(items) ⇒ Object

An alternate form of contain_exactly that accepts the expected contents as a single array arg rather that splatted out as individual items.

Examples:

expect(results).to contain_exactly(1, 2)
# is identical to:
expect(results).to match_array([1, 2])

See Also:



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# File 'lib/rspec/matchers.rb', line 706

def match_array(items)
  contain_exactly(*items)
end

#output(expected = nil) ⇒ Object

Note:

to_stdout and to_stderr work by temporarily replacing $stdout or $stderr, so they're not able to intercept stream output that explicitly uses STDOUT/STDERR or that uses a reference to $stdout/$stderr that was stored before the matcher was used.

Note:

to_stdout_from_any_process and to_stderr_from_any_process use Tempfiles, and are thus significantly (~30x) slower than to_stdout and to_stderr.

With no arg, passes if the block outputs to_stdout or to_stderr. With a string, passes if the block outputs that specific string to_stdout or to_stderr. With a regexp or matcher, passes if the block outputs a string to_stdout or to_stderr that matches.

To capture output from any spawned subprocess as well, use to_stdout_from_any_process or to_stderr_from_any_process. Output from any process that inherits the main process's corresponding standard stream will be captured.

Examples:

expect { print 'foo' }.to output.to_stdout
expect { print 'foo' }.to output('foo').to_stdout
expect { print 'foo' }.to output(/foo/).to_stdout

expect { do_something }.to_not output.to_stdout

expect { warn('foo') }.to output.to_stderr
expect { warn('foo') }.to output('foo').to_stderr
expect { warn('foo') }.to output(/foo/).to_stderr

expect { do_something }.to_not output.to_stderr

expect { system('echo foo') }.to output("foo\n").to_stdout_from_any_process
expect { system('echo foo', out: :err) }.to output("foo\n").to_stderr_from_any_process


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# File 'lib/rspec/matchers.rb', line 740

def output(expected=nil)
  BuiltIn::Output.new(expected)
end

#raise_error(error = nil, message = nil, &block) ⇒ Object Also known as: raise_exception

With no args, matches if any error is raised. With a named error, matches only if that specific error is raised. With a named error and messsage specified as a String, matches only if both match. With a named error and messsage specified as a Regexp, matches only if both match. Pass an optional block to perform extra verifications on the exception matched

Examples:

expect { do_something_risky }.to raise_error
expect { do_something_risky }.to raise_error(PoorRiskDecisionError)
expect { do_something_risky }.to raise_error(PoorRiskDecisionError) { |error| expect(error.data).to eq 42 }
expect { do_something_risky }.to raise_error(PoorRiskDecisionError, "that was too risky")
expect { do_something_risky }.to raise_error(PoorRiskDecisionError, /oo ri/)

expect { do_something_risky }.not_to raise_error


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# File 'lib/rspec/matchers.rb', line 759

def raise_error(error=nil, message=nil, &block)
  BuiltIn::RaiseError.new(error, message, &block)
end

#respond_to(*names) ⇒ Object

Matches if the target object responds to all of the names provided. Names can be Strings or Symbols.

Examples:

expect("string").to respond_to(:length)


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# File 'lib/rspec/matchers.rb', line 778

def respond_to(*names)
  BuiltIn::RespondTo.new(*names)
end

#respond_to?(method) ⇒ Boolean

:nocov:

Returns:

  • (Boolean)


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# File 'lib/rspec/matchers.rb', line 964

def respond_to?(method, *)
  method = method.to_s
  method =~ DYNAMIC_MATCHER_REGEX || super
end

#satisfy(description = "satisfy block", &block) ⇒ Object

Passes if the submitted block returns true. Yields target to the block.

Generally speaking, this should be thought of as a last resort when you can't find any other way to specify the behaviour you wish to specify.

If you do find yourself in such a situation, you could always write a custom matcher, which would likely make your specs more expressive.

Examples:

expect(5).to satisfy { |n| n > 3 }
expect(5).to satisfy("be greater than 3") { |n| n > 3 }

Parameters:

  • description (String) (defaults to: "satisfy block")

    optional description to be used for this matcher.



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# File 'lib/rspec/matchers.rb', line 799

def satisfy(description="satisfy block", &block)
  BuiltIn::Satisfy.new(description, &block)
end

#start_with(*expected) ⇒ Object

Matches if the actual value starts with the expected value(s). In the case of a string, matches against the first expected.length characters of the actual string. In the case of an array, matches against the first expected.length elements of the actual array.

Examples:

expect("this string").to   start_with "this s"
expect([0, 1, 2, 3, 4]).to start_with 0
expect([0, 2, 3, 4, 4]).to start_with 0, 1


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# File 'lib/rspec/matchers.rb', line 814

def start_with(*expected)
  BuiltIn::StartWith.new(*expected)
end

#throw_symbol(expected_symbol = nil, expected_arg = nil) ⇒ Object

Given no argument, matches if a proc throws any Symbol.

Given a Symbol, matches if the given proc throws the specified Symbol.

Given a Symbol and an arg, matches if the given proc throws the specified Symbol with the specified arg.

Examples:

expect { do_something_risky }.to throw_symbol
expect { do_something_risky }.to throw_symbol(:that_was_risky)
expect { do_something_risky }.to throw_symbol(:that_was_risky, 'culprit')

expect { do_something_risky }.not_to throw_symbol
expect { do_something_risky }.not_to throw_symbol(:that_was_risky)
expect { do_something_risky }.not_to throw_symbol(:that_was_risky, 'culprit')


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# File 'lib/rspec/matchers.rb', line 836

def throw_symbol(expected_symbol=nil, expected_arg=nil)
  BuiltIn::ThrowSymbol.new(expected_symbol, expected_arg)
end

#yield_controlObject

Note:

Your expect block must accept a parameter and pass it on to the method-under-test as a block.

Passes if the method called in the expect block yields, regardless of whether or not arguments are yielded.

Examples:

expect { |b| 5.tap(&b) }.to yield_control
expect { |b| "a".to_sym(&b) }.not_to yield_control


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# File 'lib/rspec/matchers.rb', line 857

def yield_control
  BuiltIn::YieldControl.new
end

#yield_successive_args(*args) ⇒ Object

Note:

Your expect block must accept a parameter and pass it on to the method-under-test as a block.

Designed for use with methods that repeatedly yield (such as iterators). Passes if the method called in the expect block yields multiple times with arguments matching those given.

Argument matching is done using === (the case match operator) and ==. If the expected and actual arguments match with either operator, the matcher will pass.

Examples:

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])
expect { |b| [1, 2, 3].each(&b) }.not_to yield_successive_args(1, 2)


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# File 'lib/rspec/matchers.rb', line 926

def yield_successive_args(*args)
  BuiltIn::YieldSuccessiveArgs.new(*args)
end

#yield_with_args(*args) ⇒ Object

Note:

Your expect block must accept a parameter and pass it on to the method-under-test as a block.

Note:

This matcher is not designed for use with methods that yield multiple times.

Given no arguments, matches if the method called in the expect block yields with arguments (regardless of what they are or how many there are).

Given arguments, matches if the method called in the expect block yields with arguments that match the given arguments.

Argument matching is done using === (the case match operator) and ==. If the expected and actual arguments match with either operator, the matcher will pass.

Examples:

expect { |b| 5.tap(&b) }.to yield_with_args # because #tap yields an arg
expect { |b| 5.tap(&b) }.to yield_with_args(5) # because 5 == 5
expect { |b| 5.tap(&b) }.to yield_with_args(Integer) # because Integer === 5
expect { |b| File.open("f.txt", &b) }.to yield_with_args(/txt/) # because /txt/ === "f.txt"

expect { |b| User.transaction(&b) }.not_to yield_with_args # because it yields no args
expect { |b| 5.tap(&b) }.not_to yield_with_args(1, 2, 3)


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# File 'lib/rspec/matchers.rb', line 905

def yield_with_args(*args)
  BuiltIn::YieldWithArgs.new(*args)
end

#yield_with_no_argsObject

Note:

Your expect block must accept a parameter and pass it on to the method-under-test as a block.

Note:

This matcher is not designed for use with methods that yield multiple times.

Passes if the method called in the expect block yields with no arguments. Fails if it does not yield, or yields with arguments.

Examples:

expect { |b| User.transaction(&b) }.to yield_with_no_args
expect { |b| 5.tap(&b) }.not_to yield_with_no_args # because it yields with `5`
expect { |b| "a".to_sym(&b) }.not_to yield_with_no_args # because it does not yield


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# File 'lib/rspec/matchers.rb', line 875

def yield_with_no_args
  BuiltIn::YieldWithNoArgs.new
end