module RSpec::Matchers

RSpec::Matchers provides a number of useful matchers we use to define expectations. Any object that implements the [matcher protocol](Matchers/MatcherProtocol) 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 addition 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 {RSpec::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 {RSpec::Matchers::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 {RSpec::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 {RSpec::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`.

Constants

BE_PREDICATE_REGEX
DYNAMIC_MATCHER_REGEX
HAS_REGEX

Attributes

last_expectation_handler [RW]

@private

last_matcher [RW]

@private

Public Class Methods

alias_matcher (*args, &block)

@!macro [attach] alias_matcher

@!parse
  alias $1 $2

@!visibility private We define this override here so we can attach a YARD macro to it. It ensures that our docs list all the matcher aliases.

Calls superclass method

# File rspec-expectations/lib/rspec/matchers.rb, line 250
def self.alias_matcher(*args, &block)
  super(*args, &block)
end

clear_generated_description ()

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

# File rspec-expectations/lib/rspec/matchers/generated_descriptions.rb, line 11
def self.clear_generated_description
  self.last_matcher = nil
  self.last_expectation_handler = nil
end

configuration ()

Delegates to {RSpec::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. @return [RSpec::Expectations::Configuration] the configuration object

# File rspec-expectations/lib/rspec/matchers.rb, line 951
def self.configuration
  Expectations.configuration
end

generated_description ()

@api private Generates an an example description based on the last expectation. Used by rspec-core’s one-liner syntax.

# File rspec-expectations/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

is_a_describable_matcher? (obj)

@api private

# File rspec-expectations/lib/rspec/matchers.rb, line 1008
def self.is_a_describable_matcher?(obj)
  is_a_matcher?(obj) && obj.respond_to?(:description)
end

is_a_matcher? (obj)

@api private

# File rspec-expectations/lib/rspec/matchers.rb, line 988
def self.is_a_matcher?(obj)
  return true  if ::RSpec::Matchers::BuiltIn::BaseMatcher === obj
  begin
    return false if obj.respond_to?(:i_respond_to_everything_so_im_not_really_a_matcher)
  rescue NoMethodError
    # Some objects, like BasicObject, don't implemented standard
    # reflection methods.
    return false
  end
  return false unless obj.respond_to?(:matches?)

  obj.respond_to?(:failure_message) ||
  obj.respond_to?(:failure_message_for_should) # support legacy matchers
end

last_description ()

@private

# File rspec-expectations/lib/rspec/matchers/generated_descriptions.rb, line 25
    def self.last_description
      last_matcher.respond_to?(:description) ? last_matcher.description : <<-MESSAGE
When you call a matcher in an example without a String, like this:

specify { expect(object).to matcher }

or this:

it { is_expected.to matcher }

RSpec expects the matcher to have a #description method. You should either
add a String to the example this matcher is being used in, or give it a
description method. Then you won't have to suffer this lengthy warning again.
MESSAGE
    end

Public Instance Methods

aggregate_failures (label=nil, metadata={}, &block)

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).

@param label [String] label for this aggregation block, which will be

included in the aggregated exception message.

@param metadata [Hash] 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.

@yield 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.

@raise [Expectations::MultipleExpectationsNotMetError] raised when

multiple expectations fail.

@raise [Expectations::ExpectationNotMetError] raised when a single

expectation fails.

@raise [Exception] other sorts of exceptions will be raised as normal.

@example

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

@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.

# File rspec-expectations/lib/rspec/matchers.rb, line 305
def aggregate_failures(label=nil, metadata={}, &block)
  Expectations::FailureAggregator.new(label, metadata).aggregate(&block)
end

all (expected)

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

@example

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

@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.

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 662
def all(expected)
  BuiltIn::All.new(expected)
end

be (*args)

@example

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)

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.

# File rspec-expectations/lib/rspec/matchers.rb, line 349
def be(*args)
  args.empty? ? Matchers::BuiltIn::Be.new : equal(*args)
end

be_a (klass)

passes if target.kind_of?(klass)

# File rspec-expectations/lib/rspec/matchers.rb, line 355
def be_a(klass)
  be_a_kind_of(klass)
end

Also aliased as: be_an

be_a_kind_of (expected)

Passes if actual.kind_of?(expected)

@example

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)

# File rspec-expectations/lib/rspec/matchers.rb, line 378
def be_a_kind_of(expected)
  BuiltIn::BeAKindOf.new(expected)
end

Also aliased as: be_kind_of

be_an (klass)

Alias for: be_a

be_an_instance_of (expected)

Passes if actual.instance_of?(expected)

@example

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)

# File rspec-expectations/lib/rspec/matchers.rb, line 366
def be_an_instance_of(expected)
  BuiltIn::BeAnInstanceOf.new(expected)
end

Also aliased as: be_instance_of

be_between (min, max)

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.

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 395
def be_between(min, max)
  BuiltIn::BeBetween.new(min, max)
end

be_falsey ()

Passes if actual is falsey (false or nil)

# File rspec-expectations/lib/rspec/matchers.rb, line 316
def be_falsey
  BuiltIn::BeFalsey.new
end

be_instance_of (expected)

Alias for: be_an_instance_of

be_kind_of (expected)

Alias for: be_a_kind_of

be_nil ()

Passes if actual is nil

# File rspec-expectations/lib/rspec/matchers.rb, line 324
def be_nil
  BuiltIn::BeNil.new
end

be_truthy ()

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

# File rspec-expectations/lib/rspec/matchers.rb, line 310
def be_truthy
  BuiltIn::BeTruthy.new
end

be_within (delta)

Passes if actual == expected +/- delta

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 405
def be_within(delta)
  BuiltIn::BeWithin.new(delta)
end

change (receiver=nil, message=nil, &block)

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

@param [Object] receiver @param [Symbol] message the message to send the receiver

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`

@example

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)

Notes¶ ↑

Evaluates ‘receiver.message` or `block` before and after it evaluates the block passed to `expect`. If the value is the same object, its before/after `hash` value is used to see if it has changed. Therefore, your object needs to properly implement `hash` to work correctly with this matcher.

‘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`.

# File rspec-expectations/lib/rspec/matchers.rb, line 492
def change(receiver=nil, message=nil, &block)
  BuiltIn::Change.new(receiver, message, &block)
end

contain_exactly (*items)

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.

@note This is also available using the ‘=~` operator with `should`,

but `=~` is not supported with `expect`.

@example

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

@see match_array

# File rspec-expectations/lib/rspec/matchers.rb, line 510
def contain_exactly(*items)
  BuiltIn::ContainExactly.new(items)
end

cover (*values)

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.

@example

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

### Warning: Ruby >= 1.9 only

# File rspec-expectations/lib/rspec/matchers.rb, line 528
def cover(*values)
  BuiltIn::Cover.new(*values)
end

end_with (*expected)

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.

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 543
def end_with(*expected)
  BuiltIn::EndWith.new(*expected)
end

eq (expected)

Passes if actual == expected.

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

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 558
def eq(expected)
  BuiltIn::Eq.new(expected)
end

eql (expected)

Passes if ‘actual.eql?(expected)`

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

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 572
def eql(expected)
  BuiltIn::Eql.new(expected)
end

equal (expected)

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

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

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 586
def equal(expected)
  BuiltIn::Equal.new(expected)
end

exist (*args)

Passes if ‘actual.exist?` or `actual.exists?`

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 596
def exist(*args)
  BuiltIn::Exist.new(*args)
end

have_attributes (expected)

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

@example

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) )

@note It will fail if actual doesn’t respond to any of the expected attributes.

@example

expect(person).to have_attributes(:color => "red")

# File rspec-expectations/lib/rspec/matchers.rb, line 616
def have_attributes(expected)
  BuiltIn::HaveAttributes.new(expected)
end

include (*expected)

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.

@example

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)

# File rspec-expectations/lib/rspec/matchers.rb, line 639
def include(*expected)
  BuiltIn::Include.new(*expected)
end

match (expected)

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.

@example

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

@example

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) }
  }
)

@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.

# File rspec-expectations/lib/rspec/matchers.rb, line 697
def match(expected)
  BuiltIn::Match.new(expected)
end

match_array (items)

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

@example

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

@see contain_exactly

# File rspec-expectations/lib/rspec/matchers.rb, line 715
def match_array(items)
  contain_exactly(*items)
end

output (expected=nil)

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.

@example

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

@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`.

# File rspec-expectations/lib/rspec/matchers.rb, line 752
def output(expected=nil)
  BuiltIn::Output.new(expected)
end

raise_error (error=BuiltIn::RaiseError::UndefinedValue, message=nil, &block)

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 message specified as a String, matches only if both match. With a named error and message specified as a Regexp, matches only if both match. Pass an optional block to perform extra verifications on the exception matched

@example

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 { |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 }.to raise_error("that was too risky")

expect { do_something_risky }.not_to raise_error

# File rspec-expectations/lib/rspec/matchers.rb, line 773
def raise_error(error=BuiltIn::RaiseError::UndefinedValue, message=nil, &block)
  BuiltIn::RaiseError.new(error, message, &block)
end

Also aliased as: raise_exception

raise_exception (error=BuiltIn::RaiseError::UndefinedValue, message=nil, &block)

Alias for: raise_error

respond_to (*names)

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

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 792
def respond_to(*names)
  BuiltIn::RespondTo.new(*names)
end

satisfy (description=nil, &block)

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.

@param description [String] optional description to be used for this matcher.

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 813
def satisfy(description=nil, &block)
  BuiltIn::Satisfy.new(description, &block)
end

start_with (*expected)

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.

@example

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

# File rspec-expectations/lib/rspec/matchers.rb, line 828
def start_with(*expected)
  BuiltIn::StartWith.new(*expected)
end

throw_symbol (expected_symbol=nil, expected_arg=nil)

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.

@example

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')

# File rspec-expectations/lib/rspec/matchers.rb, line 850
def throw_symbol(expected_symbol=nil, expected_arg=nil)
  BuiltIn::ThrowSymbol.new(expected_symbol, expected_arg)
end

yield_control ()

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

@example

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

@note Your expect block must accept a parameter and pass it on to

the method-under-test as a block.

# File rspec-expectations/lib/rspec/matchers.rb, line 871
def yield_control
  BuiltIn::YieldControl.new
end

yield_successive_args (*args)

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.

@example

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)

@note Your expect block must accept a parameter and pass it on to

the method-under-test as a block.

# File rspec-expectations/lib/rspec/matchers.rb, line 940
def yield_successive_args(*args)
  BuiltIn::YieldSuccessiveArgs.new(*args)
end

yield_with_args (*args)

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.

@example

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)

@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.

# File rspec-expectations/lib/rspec/matchers.rb, line 919
def yield_with_args(*args)
  BuiltIn::YieldWithArgs.new(*args)
end

yield_with_no_args ()

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

@example

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

@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.

# File rspec-expectations/lib/rspec/matchers.rb, line 889
def yield_with_no_args
  BuiltIn::YieldWithNoArgs.new
end