Module: Spec::Matchers

Module | Spec::Matchers
In: | lib/spec/matchers/be.rb lib/spec/matchers/be_close.rb lib/spec/matchers/change.rb lib/spec/matchers/eql.rb lib/spec/matchers/equal.rb lib/spec/matchers/exist.rb lib/spec/matchers/has.rb lib/spec/matchers/have.rb lib/spec/matchers/include.rb lib/spec/matchers/match.rb lib/spec/matchers/operator_matcher.rb lib/spec/matchers/raise_error.rb lib/spec/matchers/respond_to.rb lib/spec/matchers/satisfy.rb lib/spec/matchers/simple_matcher.rb lib/spec/matchers/throw_symbol.rb lib/spec/matchers.rb

RSpec ships with a number of useful Expression Matchers. An Expression Matcher is any object that responds to the following methods:

      matches?(actual)
      failure_message
      negative_failure_message #optional
      description #optional

See Spec::Expectations to learn how to use these as Expectation Matchers. See Spec::Mocks to learn how to use them as Mock Argument Constraints.

## 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 Expectation Matchers

When you find that none of the stock Expectation Matchers provide a natural feeling expectation, you can very easily write your own.

For example, 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")

To do this, you would need to write a class like this:

      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 negative_failure_message
          "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 `require`d from your spec file(s):

      Spec::Runner.configure do |config|
        config.include(CustomGameMatchers)
      end

### Methods

be be_close change eql equal exist have have_at_least have_at_most have_exactly include match raise_error respond_to satisfy simple_matcher throw_symbol

### Classes and Modules

Module Spec::Matchers::ModuleMethods
Class Spec::Matchers::BaseOperatorMatcher
Class Spec::Matchers::Exist
Class Spec::Matchers::MatcherError
Class Spec::Matchers::SimpleMatcher

### Public Instance methods

should be
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 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
      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?
      "this string".should be_an_intance_of(String)

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

[Source]

         # File lib/spec/matchers/be.rb, line 220
    220:     def be(*args)
    221:       Matchers::Be.new(*args)
    222:     end

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)

[Source]

        # File lib/spec/matchers/be_close.rb, line 33
    33:     def be_close(expected, delta)
    34:       Matchers::BeClose.new(expected, delta)
    35:     end

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)

[Source]

         # File lib/spec/matchers/change.rb, line 141
    141:     def change(target=nil, message=nil, &block)
    142:       Matchers::Change.new(target, message, &block)
    143:     end

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)

[Source]

        # File lib/spec/matchers/eql.rb, line 39
    39:     def eql(expected)
    40:       Matchers::Eql.new(expected)
    41:     end

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

[Source]

        # File lib/spec/matchers/equal.rb, line 39
    39:     def equal(expected)
    40:       Matchers::Equal.new(expected)
    41:     end

exist()

[Source]

        # File lib/spec/matchers/exist.rb, line 15
    15:     def exist; Exist.new; end

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

[Source]

         # File lib/spec/matchers/have.rb, line 118
    118:     def have(n)
    119:       Matchers::Have.new(n)
    120:     end

should have_at_least(number).items

Exactly like have() with >=.

## Warning

`should_not` `have_at_least` is not supported

[Source]

         # File lib/spec/matchers/have.rb, line 131
    131:     def have_at_least(n)
    132:       Matchers::Have.new(n, :at_least)
    133:     end

should have_at_most(number).items

Exactly like have() with <=.

## Warning

`should_not` `have_at_most` is not supported

[Source]

         # File lib/spec/matchers/have.rb, line 143
    143:     def have_at_most(n)
    144:       Matchers::Have.new(n, :at_most)
    145:     end

have_exactly(n)

Alias for have

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")

[Source]

        # File lib/spec/matchers/include.rb, line 66
    66:     def include(*expected)
    67:       Matchers::Include.new(*expected)
    68:     end

should match(regexp)
should_not match(regexp)

Given a Regexp, passes if actual =~ regexp

## Examples

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

[Source]

        # File lib/spec/matchers/match.rb, line 37
    37:     def match(regexp)
    38:       Matchers::Match.new(regexp)
    39:     end

should raise_error()
should raise_error(NamedError)
should raise_error(NamedError, String)
should raise_error(NamedError, Regexp)
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.

## Examples

      lambda { do_something_risky }.should raise_error
      lambda { do_something_risky }.should raise_error(PoorRiskDecisionError)
      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/)

[Source]

         # File lib/spec/matchers/raise_error.rb, line 105
    105:     def raise_error(error=Exception, message=nil)
    106:       Matchers::RaiseError.new(error, message)
    107:     end

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

[Source]

        # File lib/spec/matchers/respond_to.rb, line 41
    41:     def respond_to(*names)
    42:       Matchers::RespondTo.new(*names)
    43:     end

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
      }

[Source]

        # File lib/spec/matchers/satisfy.rb, line 43
    43:     def satisfy(&block)
    44:       Matchers::Satisfy.new(&block)
    45:     end

simple_matcher(message, &match_block)

[Source]

        # File lib/spec/matchers/simple_matcher.rb, line 25
    25:     def simple_matcher(message, &match_block)
    26:       SimpleMatcher.new(message, &match_block)
    27:     end

should throw_symbol()
should throw_symbol(:sym)
should_not throw_symbol()
should_not throw_symbol(:sym)

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

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

## Examples

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

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

[Source]

        # File lib/spec/matchers/throw_symbol.rb, line 70
    70:     def throw_symbol(sym=nil)
    71:       Matchers::ThrowSymbol.new(sym)
    72:     end

[Validate]