Module: RSpec::Matchers

Included in:
DSL::Matcher
Defined in:
lib/rspec/matchers.rb,
lib/rspec/matchers/dsl.rb,
lib/rspec/matchers/pretty.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/built_in/match.rb,
lib/rspec/matchers/built_in/cover.rb,
lib/rspec/matchers/built_in/yield.rb,
lib/rspec/matchers/built_in/exist.rb,
lib/rspec/matchers/built_in/equal.rb,
lib/rspec/matchers/built_in/output.rb,
lib/rspec/matchers/aliased_matcher.rb,
lib/rspec/matchers/built_in/change.rb,
lib/rspec/matchers/matcher_protocol.rb,
lib/rspec/matchers/built_in/include.rb,
lib/rspec/matchers/built_in/satisfy.rb,
lib/rspec/matchers/built_in/compound.rb,
lib/rspec/matchers/matcher_delegator.rb,
lib/rspec/matchers/built_in/operators.rb,
lib/rspec/matchers/built_in/be_within.rb,
lib/rspec/matchers/built_in/respond_to.rb,
lib/rspec/matchers/built_in/be_between.rb,
lib/rspec/matchers/built_in/be_kind_of.rb,
lib/rspec/matchers/built_in/raise_error.rb,
lib/rspec/matchers/built_in/throw_symbol.rb,
lib/rspec/matchers/built_in/base_matcher.rb,
lib/rspec/matchers/generated_descriptions.rb,
lib/rspec/matchers/built_in/be_instance_of.rb,
lib/rspec/matchers/built_in/have_attributes.rb,
lib/rspec/matchers/built_in/contain_exactly.rb,
lib/rspec/matchers/built_in/start_and_end_with.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 "bean", 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(Fixnum)        # => 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(Fixnum)   # => 3.instance_of?(Fixnum)  | 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)

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.

Defined Under Namespace

Modules: BuiltIn, Composable, DSL, Pretty Classes: AliasedMatcher, MatcherProtocol

Constant Summary

Class Method Summary (collapse)

Instance Method Summary (collapse)

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

- (Object) method_missing(method, *args, &block) (private) 

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# File 'lib/rspec/matchers.rb', line 931
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

+ (Object) alias_matcher(new_name, old_name, options = {}) {|String| ... }

Defines a matcher alias. The returned matcher's description will be overriden to reflect the phrasing of the new name, which will be used in failure messages when passed as an argument to another matcher in a composed matcher expression.

Examples:


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"

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"

Parameters:

  • new_name (Symbol) —

    the new name for the matcher

  • old_name (Symbol) —

    the original name for the matcher

  • options (Hash) (defaults to: {}) —

    options for the aliased matcher

Options Hash (options):

  • :klass (Class) —

    the ruby class to use as the decorator. (Not normally used).

Yields:

  • (String) —

    optional block that, when given is used to define the overriden description. The yielded arg is the original description. If no block is provided, a default description override is used based on the old and new names.

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# File 'lib/rspec/matchers.rb', line 246
def self.alias_matcher(new_name, old_name, options={}, &description_override)
  description_override ||= lambda do |old_desc|
    old_desc.gsub(Pretty.split_words(old_name), Pretty.split_words(new_name))
  end
  klass = options.fetch(:klass) { AliasedMatcher }
  define_method(new_name) do |*args, &block|
    matcher = __send__(old_name, *args, &block)
    klass.new(matcher, description_override)
  end
end

+ (Object) clear_generated_description

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

+ (RSpec::Expectations::Configuration) 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 922
def self.configuration
  Expectations.configuration
end

+ (Object) define_negated_matcher(negated_name, base_name) {|String| ... }

Defines a negated matcher. The returned matcher's description and failure_message will be overriden to reflect the phrasing of the new name, and the match logic will be based on the original matcher but negated.

Examples:


RSpec::Matchers.define_negated_matcher :a_value_not_between, :a_value_between
a_value_between(3, 5).description # => "a value between 3 and 5"
a_value_not_between(3, 5).description # => "a value not between 3 and 5"

Parameters:

  • negated_name (Symbol) —

    the name for the negated matcher

  • base_name (Symbol) —

    the name of the original matcher that will be negated

Yields:

  • (String) —

    optional block that, when given is used to define the overriden description. The yielded arg is the original description. If no block is provided, a default description override is used based on the old and new names.

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# File 'lib/rspec/matchers.rb', line 274
def self.define_negated_matcher(negated_name, base_name, &description_override)
  alias_matcher(negated_name, base_name, :klass => AliasedNegatedMatcher, &description_override)
end

+ (Object) generated_description

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

- (Object) all(expected)

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 actual all expected objects pass. This works for any enumerable object.

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 635
def all(expected)
  BuiltIn::All.new(expected)
end

- (Object) be(*args) Also known as: a_value

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 arbitrarypredicate feature will handle any predicate prefixed with "be_an" (e.g. bean_instance_of), "be_a" (e.g. bea_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 318
def be(*args)
  args.empty? ? Matchers::BuiltIn::Be.new : equal(*args)
end

- (Object) be_a(klass) Also known as: be_an

passes if target.kind_of?(klass)

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# File 'lib/rspec/matchers.rb', line 324
def be_a(klass)
  be_a_kind_of(klass)
end

- (Object) be_a_kind_of(expected) Also known as: be_kind_of, a_kind_of

Passes if actual.kind_of?(expected)

Examples:


expect(5).to     be_a_kind_of(Fixnum)
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 349
def be_a_kind_of(expected)
  BuiltIn::BeAKindOf.new(expected)
end

- (Object) be_an_instance_of(expected) Also known as: be_instance_of, an_instance_of

Passes if actual.instance_of?(expected)

Examples:


expect(5).to     be_an_instance_of(Fixnum)
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 336
def be_an_instance_of(expected)
  BuiltIn::BeAnInstanceOf.new(expected)
end

- (Object) be_between(min, max) Also known as: a_value_between

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 367
def be_between(min, max)
  BuiltIn::BeBetween.new(min, max)
end

- (Object) be_falsey Also known as: be_falsy, a_falsey_value, a_falsy_value

Passes if actual is falsey (false or nil)

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# File 'lib/rspec/matchers.rb', line 285
def be_falsey
  BuiltIn::BeFalsey.new
end

- (Object) be_nil Also known as: a_nil_value

Passes if actual is nil

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# File 'lib/rspec/matchers.rb', line 293
def be_nil
  BuiltIn::BeNil.new
end

- (Object) be_truthy Also known as: a_truthy_value

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

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# File 'lib/rspec/matchers.rb', line 279
def be_truthy
  BuiltIn::BeTruthy.new
end

- (Object) be_within(delta) Also known as: a_value_within, within

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 378
def be_within(delta)
  BuiltIn::BeWithin.new(delta)
end

- (Object) change(receiver = nil, message = nil, &block) Also known as: a_block_changing, changing

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 463
def change(receiver=nil, message=nil, &block)
  BuiltIn::Change.new(receiver, message, &block)
end

- (Object) contain_exactly(*items) Also known as: a_collection_containing_exactly, containing_exactly

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 482
def contain_exactly(*items)
  BuiltIn::ContainExactly.new(items)
end

- (Object) cover(*values) Also known as: a_range_covering, covering

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 500
def cover(*values)
  BuiltIn::Cover.new(*values)
end

- (Object) end_with(*expected) Also known as: a_collection_ending_with, a_string_ending_with, ending_with

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 516
def end_with(*expected)
  BuiltIn::EndWith.new(*expected)
end

- (Object) eq(expected) Also known as: an_object_eq_to, eq_to

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 532
def eq(expected)
  BuiltIn::Eq.new(expected)
end

- (Object) eql(expected) Also known as: an_object_eql_to, eql_to

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 547
def eql(expected)
  BuiltIn::Eql.new(expected)
end

- (Object) equal(expected) Also known as: an_object_equal_to, equal_to

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)   # Fixnums 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 562
def equal(expected)
  BuiltIn::Equal.new(expected)
end

- (Object) exist(*args) Also known as: an_object_existing, existing

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 572
def exist(*args)
  BuiltIn::Exist.new(*args)
end

- (ExpectationTarget) expect

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 205


    		
  





      

  

    - (Object) have_attributes(expected) 
    Also known as:
    an_object_having_attributes
    


  

  

    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 594
def have_attributes(expected)
  BuiltIn::HaveAttributes.new(expected)
end

    		
  





      

  

    - (Object) include(*expected) 
    Also known as:
    a_collection_including, a_string_including, a_hash_including, including
    


  

    
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")

  



  

    
      
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# File 'lib/rspec/matchers.rb', line 611
def include(*expected)
  BuiltIn::Include.new(*expected)
end

    		
  





      

  

    - (Object) match(expected) 
    Also known as:
    match_regex, an_object_matching, a_string_matching, matching
    


  

  

    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(Fixnum)
    ),
    :c => { :d => (a_value < 3) }
  }
)

  



  

    
      
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# File 'lib/rspec/matchers.rb', line 672
def match(expected)
  BuiltIn::Match.new(expected)
end

    		
  





      

  

    - (Object) match_array(items) 


  

    
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 691
def match_array(items)
  contain_exactly(*items)
end

    		
  





      

  

    - (Object) output(expected = nil) 
    Also known as:
    a_block_outputting
    


  

  

    Note:
    
This matcher works by temporarily replacing $stdout or $stderr,
so it's 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 is used.



  


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

  





  

    
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

  



  

    
      
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# File 'lib/rspec/matchers.rb', line 717
def output(expected=nil)
  BuiltIn::Output.new(expected)
end

    		
  





      

  

    - (Object) raise_error(error = Exception, message = nil, &block) 
    Also known as:
    raise_exception, a_block_raising, raising
    


  

    
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 737
def raise_error(error=Exception, message=nil, &block)
  BuiltIn::RaiseError.new(error, message, &block)
end

    		
  





      

  

    - (Object) respond_to(*names) 
    Also known as:
    an_object_responding_to, responding_to
    


  

    
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 757
def respond_to(*names)
  BuiltIn::RespondTo.new(*names)
end

    		
  





      

  

    - (Object) satisfy(&block) 
    Also known as:
    an_object_satisfying, satisfying
    


  

    
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 }

  



  

    
      
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# File 'lib/rspec/matchers.rb', line 776
def satisfy(&block)
  BuiltIn::Satisfy.new(&block)
end

    		
  





      

  

    - (Object) start_with(*expected) 
    Also known as:
    a_collection_starting_with, a_string_starting_with, starting_with
    


  

    
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 792
def start_with(*expected)
  BuiltIn::StartWith.new(*expected)
end

    		
  





      

  

    - (Object) throw_symbol(expected_symbol = nil, expected_arg = nil) 
    Also known as:
    a_block_throwing, throwing
    


  

    
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 815
def throw_symbol(expected_symbol=nil, expected_arg=nil)
  BuiltIn::ThrowSymbol.new(expected_symbol, expected_arg)
end

    		
  





      

  

    - (Object) yield_control 
    Also known as:
    a_block_yielding_control, yielding_control
    


  

  

    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, 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 839
def yield_control
  BuiltIn::YieldControl.new
end

    		
  





      

  

    - (Object) yield_successive_args(*args) 
    Also known as:
    a_block_yielding_successive_args, yielding_successive_args
    


  

  

    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 911
def yield_successive_args(*args)
  BuiltIn::YieldSuccessiveArgs.new(*args)
end

    		
  





      

  

    - (Object) yield_with_args(*args) 
    Also known as:
    a_block_yielding_with_args, yielding_with_args
    


  

  

    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(Fixnum) # because Fixnum === 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 889
def yield_with_args(*args)
  BuiltIn::YieldWithArgs.new(*args)
end

    		
  





      

  

    - (Object) yield_with_no_args 
    Also known as:
    a_block_yielding_with_no_args, yielding_with_no_args
    


  

  

    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 858
def yield_with_no_args
  BuiltIn::YieldWithNoArgs.new
end