Module: RSpec::Matchers

Included in:
Matcher
Defined in:
lib/rspec/matchers.rb,
lib/rspec/matchers/be.rb,
lib/rspec/matchers/eq.rb,
lib/rspec/matchers/dsl.rb,
lib/rspec/matchers/eql.rb,
lib/rspec/matchers/has.rb,
lib/rspec/matchers/have.rb,
lib/rspec/matchers/equal.rb,
lib/rspec/matchers/exist.rb,
lib/rspec/matchers/match.rb,
lib/rspec/matchers/change.rb,
lib/rspec/matchers/errors.rb,
lib/rspec/matchers/pretty.rb,
lib/rspec/matchers/include.rb,
lib/rspec/matchers/matcher.rb,
lib/rspec/matchers/satisfy.rb,
lib/rspec/matchers/be_close.rb,
lib/rspec/matchers/be_kind_of.rb,
lib/rspec/matchers/respond_to.rb,
lib/rspec/matchers/match_array.rb,
lib/rspec/matchers/raise_error.rb,
lib/rspec/matchers/throw_symbol.rb,
lib/rspec/matchers/be_instance_of.rb,
lib/rspec/matchers/method_missing.rb,
lib/rspec/matchers/operator_matcher.rb,
lib/rspec/matchers/generated_descriptions.rb,
lib/rspec/matchers/extensions/instance_exec.rb

Overview

rspec-expecations provides a number of useful Matchers we use to compose expectations. A Matcher is any object that responds to the following methods:

matches?(actual)
failure_message_for_should

These methods are also part of the matcher protocol, but are optional:

does_not_match?(actual)
failure_message_for_should_not
description #optional

Predicates

In addition to those Expression 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 should be_ followed by the predicate without the question mark, and RSpec will figure it out from there. For example:

[].should be_empty => [].empty? #passes
[].should_not 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:

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

3.should be_a_kind_of(Fixnum) => 3.kind_of?(Numeric) #passes
3.should be_a_kind_of(Numeric) => 3.kind_of?(Numeric) #passes
3.should be_an_instance_of(Fixnum) => 3.instance_of?(Fixnum) #passes
3.should_not be_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:

{:a => "A"}.should have_key(:a) => {:a => "A"}.has_key?(:a) #passes
{:a => "A"}.should have_key(:b) => {:a => "A"}.has_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.

Custom Matchers

When you find that none of the stock Expectation 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:

bob.current_zone.should eql(Zone.new("4"))

But you might find it more expressive to say:

bob.should be_in_zone("4")

and/or

bob.should_not 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_for_should do |player|
    # generate and return the appropriate string.
  end
  failure_message_for_should_not 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_for_should and failure_message_for_should_not) are passed the actual value (the receiver of should or should_not).

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_for_should
    "expected #{@target.inspect} to be in Zone #{@expected}"
  end
  def failure_message_for_should_not
    "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::Runner.configure do |config|
  config.include(CustomGameMatchers)
end

Defined Under Namespace

Modules: DSL, InstanceExec, Pretty Classes: Be, BeComparedTo, BePredicate, Change, Has, Have, MatchArray, Matcher, MatcherError, NegativeOperatorMatcher, OperatorMatcher, PositiveOperatorMatcher, RaiseError, RespondTo, Satisfy, ThrowSymbol

Class Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(sym, *args, &block) ⇒ Object

:nodoc:


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# File 'lib/rspec/matchers/method_missing.rb', line 3

def method_missing(sym, *args, &block) # :nodoc:
  return Matchers::BePredicate.new(sym, *args, &block) if sym.to_s =~ /^be_/
  return Matchers::Has.new(sym, *args, &block) if sym.to_s =~ /^have_/
  super
end

Class Attribute Details

.last_matcherObject

:nodoc:


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# File 'lib/rspec/matchers/generated_descriptions.rb', line 4

def last_matcher
  @last_matcher
end

.last_shouldObject

:nodoc:


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# File 'lib/rspec/matchers/generated_descriptions.rb', line 4

def last_should
  @last_should
end

Class Method Details

.clear_generated_descriptionObject


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# File 'lib/rspec/matchers/generated_descriptions.rb', line 7

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

.generated_descriptionObject


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# File 'lib/rspec/matchers/generated_descriptions.rb', line 12

def self.generated_description
  return nil if last_should.nil?
  "#{last_should.to_s.gsub('_',' ')} #{last_description}"
end

Instance Method Details

#be(*args) ⇒ Object

:call-seq:

should be_true
should be_false
should be_nil
should be_[arbitrary_predicate](*args)
should_not be_nil
should_not 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.

Examples

target.should be_true
target.should be_false
target.should be_nil
target.should_not be_nil

collection.should be_empty #passes if target.empty?
target.should_not be_empty #passes unless target.empty?
target.should_not be_old_enough(16) #passes unless target.old_enough?(16)

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# File 'lib/rspec/matchers/be.rb', line 210

def be(*args)
  args.empty? ?
    Matchers::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/be.rb', line 216

def be_a(klass)
  be_a_kind_of(klass)
end

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

:call-seq:

should be_kind_of(expected)
should be_a_kind_of(expected)
should_not be_kind_of(expected)
should_not be_a_kind_of(expected)

Passes if actual.kind_of?(expected)

Examples

5.should be_kind_of(Fixnum)
5.should be_kind_of(Numeric)
5.should_not be_kind_of(Float)

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# File 'lib/rspec/matchers/be_kind_of.rb', line 16

def be_a_kind_of(expected)
  Matcher.new :be_a_kind_of, expected do |_expected_|
    match do |actual|
      actual.kind_of?(_expected_)
    end
  end
end

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

:call-seq:

should be_instance_of(expected)
should be_an_instance_of(expected)
should_not be_instance_of(expected)
should_not be_an_instance_of(expected)

Passes if actual.instance_of?(expected)

Examples

5.should be_instance_of(Fixnum)
5.should_not be_instance_of(Numeric)
5.should_not be_instance_of(Float)

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# File 'lib/rspec/matchers/be_instance_of.rb', line 16

def be_an_instance_of(expected)
  Matcher.new :be_an_instance_of, expected do |_expected_|
    match do |actual|
      actual.instance_of?(_expected_)
    end
  end
end

#be_close(expected, delta) ⇒ Object

:call-seq:

should be_close(expected, delta)
should_not be_close(expected, delta)

Passes if actual == expected +/- delta

Example

result.should be_close(3.0, 0.5)

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# File 'lib/rspec/matchers/be_close.rb', line 12

def be_close(expected, delta)
  Matcher.new :be_close, expected, delta do |_expected_, _delta_|
    match do |actual|
      (actual - _expected_).abs < _delta_
    end

    failure_message_for_should do |actual|
      "expected #{_expected_} +/- (< #{_delta_}), got #{actual}"
    end

    failure_message_for_should_not do |actual|
      "expected #{_expected_} +/- (< #{_delta_}), got #{actual}"
    end

    description do
      "be close to #{_expected_} (within +- #{_delta_})"
    end
  end
end

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

:call-seq:

should change(receiver, message, &block)
should change(receiver, message, &block).by(value)
should change(receiver, message, &block).from(old).to(new)
should_not change(receiver, message, &block)

Allows you to specify that a Proc will cause some value to change.

Examples

lambda {
  team.add_player(player) 
}.should change(roster, :count)

lambda {
  team.add_player(player) 
}.should change(roster, :count).by(1)

lambda {
  team.add_player(player) 
}.should change(roster, :count).by_at_least(1)

lambda {
  team.add_player(player)
}.should change(roster, :count).by_at_most(1)    

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

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

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

Evaluates receiver.message or block before and after it evaluates the c object (generated by the lambdas in the examples above).

Then compares the values before and after the receiver.message and evaluates the difference compared to the expected difference.

WARNING

should_not change only supports the form with no subsequent calls to by, by_at_least, by_at_most, to or from.

blocks passed to should change and should_not change must use the {} form (do/end is not supported).


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# File 'lib/rspec/matchers/change.rb', line 180

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

#eq(expected) ⇒ Object

:call-seq:

should eq(expected)
should_not eq(expected)

Passes if actual == expected.

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

Examples

5.should eq(5)
5.should_not eq(3)

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# File 'lib/rspec/matchers/eq.rb', line 15

def eq(expected)
  Matcher.new :eq, expected do |_expected_|

    diffable

    match do |actual|
      actual == _expected_
    end

    failure_message_for_should do |actual|
      <<-MESSAGE

expected #{_expected_.inspect}
 got #{actual.inspect}

(compared using ==)
MESSAGE
    end

    failure_message_for_should_not do |actual|
      <<-MESSAGE

expected #{actual.inspect} not to equal #{_expected_.inspect}

(compared using ==)
MESSAGE
    end

    description do
      "== #{_expected_}"
    end
  end
end

#eql(expected) ⇒ Object

:call-seq:

should eql(expected)
should_not eql(expected)

Passes if actual and expected are of equal value, but not necessarily the same object.

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

Examples

5.should eql(5)
5.should_not eql(3)

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# File 'lib/rspec/matchers/eql.rb', line 15

def eql(expected)
  Matcher.new :eql, expected do |_expected_|

    diffable

    match do |actual|
      actual.eql?(_expected_)
    end

    failure_message_for_should do |actual|
      <<-MESSAGE

expected #{_expected_.inspect}
 got #{actual.inspect}

(compared using eql?)
MESSAGE
    end

    failure_message_for_should_not do |actual|
      <<-MESSAGE

expected #{actual.inspect} not to equal #{_expected_.inspect}

(compared using eql?)
MESSAGE
    end
  end
end

#equal(expected) ⇒ Object

:call-seq:

should equal(expected)
should_not equal(expected)

Passes if actual and expected are the same object (object identity).

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

Examples

5.should equal(5) #Fixnums are equal
"5".should_not equal("5") #Strings that look the same are not the same object

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# File 'lib/rspec/matchers/equal.rb', line 16

def equal(expected)
  Matcher.new :equal, expected do |_expected_|
    match do |actual|
      actual.equal?(_expected_)
    end
    
    def inspect_object(o)
      "#<#{o.class}:#{o.object_id}> => #{o.inspect}"
    end
    
    failure_message_for_should do |actual|
      <<-MESSAGE

expected #{inspect_object(_expected_)}
 got #{inspect_object(actual)}

Compared using equal?, which compares object identity,
but expected and actual are not the same object. Use
'actual.should == expected' if you don't care about
object identity in this example.

MESSAGE
    end

    failure_message_for_should_not do |actual|
      <<-MESSAGE

expected not #{inspect_object(actual)}
     got #{inspect_object(_expected_)}

Compared using equal?, which compares object identity.

MESSAGE
    end
  end
end

#exist(arg = nil) ⇒ Object

:call-seq:

should exist
should_not exist

Passes if actual.exist?


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# File 'lib/rspec/matchers/exist.rb', line 8

def exist(arg=nil)
  Matcher.new :exist do
    match do |actual|
      arg ? actual.exist?(arg) : actual.exist?
    end
  end
end

#have(n) ⇒ Object Also known as: have_exactly

:call-seq:

should have(number).named_collection__or__sugar
should_not have(number).named_collection__or__sugar

Passes if receiver is a collection with the submitted number of items OR if the receiver OWNS a collection with the submitted number of items.

If the receiver OWNS the collection, you must use the name of the collection. So if a Team instance has a collection named #players, you must use that name to set the expectation.

If the receiver IS the collection, you can use any name you like for named_collection. We'd recommend using either “elements”, “members”, or “items” as these are all standard ways of describing the things IN a collection.

This also works for Strings, letting you set an expectation about its length

Examples

# Passes if team.players.size == 11
team.should have(11).players

# Passes if [1,2,3].length == 3
[1,2,3].should have(3).items #"items" is pure sugar

# Passes if "this string".length == 11
"this string".should have(11).characters #"characters" is pure sugar

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# File 'lib/rspec/matchers/have.rb', line 122

def have(n)
  Matchers::Have.new(n)
end

#have_at_least(n) ⇒ Object

:call-seq:

should have_at_least(number).items

Exactly like have() with >=.

Warning

should_not have_at_least is not supported


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# File 'lib/rspec/matchers/have.rb', line 135

def have_at_least(n)
  Matchers::Have.new(n, :at_least)
end

#have_at_most(n) ⇒ Object

:call-seq:

should have_at_most(number).items

Exactly like have() with <=.

Warning

should_not have_at_most is not supported


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# File 'lib/rspec/matchers/have.rb', line 147

def have_at_most(n)
  Matchers::Have.new(n, :at_most)
end

#include(*expected) ⇒ Object

:call-seq:

should include(expected)
should_not 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.

Examples

[1,2,3].should include(3)
[1,2,3].should include(2,3) #would pass
[1,2,3].should include(2,3,4) #would fail
[1,2,3].should_not include(4)
"spread".should include("read")
"spread".should_not include("red")

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

def include(*expected)
  Matcher.new :include, *expected do |*_expected|
    match_for_should do |actual|
      perform_match(:all?, :all?, actual, _expected)
    end

    match_for_should_not do |actual|
      perform_match(:none?, :any?, actual, _expected)
    end

    def perform_match(predicate, hash_predicate, actual, _expected)
      _expected.send(predicate) do |expected|
        if comparing_hash_values?(actual, expected)
          expected.send(hash_predicate) {|k,v| actual[k] == v}
        elsif comparing_hash_keys?(actual, expected)
          actual.has_key?(expected)
        else
          actual.include?(expected)
        end
      end
    end

    def comparing_hash_keys?(actual, expected) # :nodoc:
      actual.is_a?(Hash) && !expected.is_a?(Hash)
    end

    def comparing_hash_values?(actual, expected) # :nodoc:
      actual.is_a?(Hash) && expected.is_a?(Hash)
    end
  end
end

#match(expected) ⇒ Object

:call-seq:

should match(pattern)
should_not match(pattern)

Given a Regexp or String, passes if actual.match(pattern)

Examples

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

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# File 'lib/rspec/matchers/match.rb', line 13

def match(expected)
  Matcher.new :match, expected do |_expected_|
    match do |actual|
      actual.match(_expected_)
    end
  end
end

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

:call-seq:

should raise_error()
should raise_error(NamedError)
should raise_error(NamedError, String)
should raise_error(NamedError, Regexp)
should raise_error() { |error| ... }
should raise_error(NamedError) { |error| ... }
should raise_error(NamedError, String) { |error| ... }
should raise_error(NamedError, Regexp) { |error| ... }
should_not raise_error()
should_not raise_error(NamedError)
should_not raise_error(NamedError, String)
should_not raise_error(NamedError, Regexp)

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

lambda { do_something_risky }.should raise_error
lambda { do_something_risky }.should raise_error(PoorRiskDecisionError)
lambda { do_something_risky }.should raise_error(PoorRiskDecisionError) { |error| error.data.should == 42 }
lambda { do_something_risky }.should raise_error(PoorRiskDecisionError, "that was too risky")
lambda { do_something_risky }.should raise_error(PoorRiskDecisionError, /oo ri/)

lambda { do_something_risky }.should_not raise_error
lambda { do_something_risky }.should_not raise_error(PoorRiskDecisionError)
lambda { do_something_risky }.should_not raise_error(PoorRiskDecisionError, "that was too risky")
lambda { do_something_risky }.should_not raise_error(PoorRiskDecisionError, /oo ri/)

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# File 'lib/rspec/matchers/raise_error.rb', line 125

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

#respond_to(*names) ⇒ Object

:call-seq:

should respond_to(*names)
should_not respond_to(*names)

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

Examples


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# File 'lib/rspec/matchers/respond_to.rb', line 81

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

#satisfy(&block) ⇒ Object

:call-seq:

should satisfy {}
should_not satisfy {}

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

5.should satisfy { |n|
  n > 3
}

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# File 'lib/rspec/matchers/satisfy.rb', line 47

def satisfy(&block)
  Matchers::Satisfy.new(&block)
end

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

:call-seq:

should throw_symbol()
should throw_symbol(:sym)
should throw_symbol(:sym, arg)
should_not throw_symbol()
should_not throw_symbol(:sym)
should_not throw_symbol(:sym, arg)

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

lambda { do_something_risky }.should throw_symbol
lambda { do_something_risky }.should throw_symbol(:that_was_risky)
lambda { do_something_risky }.should throw_symbol(:that_was_risky, culprit)

lambda { do_something_risky }.should_not throw_symbol
lambda { do_something_risky }.should_not throw_symbol(:that_was_risky)
lambda { do_something_risky }.should_not throw_symbol(:that_was_risky, culprit)

100
101
102
# File 'lib/rspec/matchers/throw_symbol.rb', line 100

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