Module Spec::Matchers
In: lib/spec/matchers.rb
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

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 required from your spec file(s):

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

Methods

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

Given true, false, or nil, will pass if given 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
  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)

Passes if given == expected +/- delta

Example

  result.should be_close(3.0, 0.5)

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).

Passes if given 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)

Passes if given 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

Passes if given.exist?

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

Exactly like have() with >=.

Warning

should_not have_at_least is not supported

Exactly like have() with <=.

Warning

should_not have_at_most is not supported

have_exactly(n)

Alias for have

Passes if given 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")

Given a Regexp, passes if given =~ regexp

Examples

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

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/)

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

Examples

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
  }

simple_matcher makes it easy for you to create your own custom matchers in just a few lines of code when you don‘t need all the power of a completely custom matcher object.

The description argument will appear as part of any failure message, and is also the source for auto-generated descriptions.

The match_block can have an arity of 1 or 2. The first block argument will be the given value. The second, if the block accepts it will be the matcher itself, giving you access to set custom failure messages in favor of the defaults.

The match_block should return a boolean: true indicates a match, which will pass if you use should and fail if you use should_not. false (or nil) indicates no match, which will do the reverse: fail if you use should and pass if you use should_not.

An error in the match_block will bubble up, resulting in a failure.

Example with default messages

  def be_even
    simple_matcher("an even number") { |given| given % 2 == 0 }
  end

  describe 2 do
    it "should be even" do
      2.should be_even
    end
  end

Given an odd number, this example would produce an error message stating: expected "an even number", got 3.

Unfortunately, if you‘re a fan of auto-generated descriptions, this will produce "should an even number." Not the most desirable result. You can control that using custom messages:

Example with custom messages

  def rhyme_with(expected)
    simple_matcher("rhyme with #{expected.inspect}") do |given, matcher|
      matcher.failure_message = "expected #{given.inspect} to rhyme with #{expected.inspect}"
      matcher.negative_failure_message = "expected #{given.inspect} not to rhyme with #{expected.inspect}"
      given.rhymes_with? expected
    end
  end

  # OR

  def rhyme_with(expected)
    simple_matcher do |given, matcher|
      matcher.description = "rhyme with #{expected.inspect}"
      matcher.failure_message = "expected #{given.inspect} to rhyme with #{expected.inspect}"
      matcher.negative_failure_message = "expected #{given.inspect} not to rhyme with #{expected.inspect}"
      given.rhymes_with? expected
    end
  end

  describe "pecan" do
    it "should rhyme with 'be gone'" do
      nut = "pecan"
      nut.extend Rhymer
      nut.should rhyme_with("be gone")
    end
  end

The resulting messages would be:

  description:              rhyme with "be gone"
  failure_message:          expected "pecan" to rhyme with "be gone"
  negative failure_message: expected "pecan" not to rhyme with "be gone"

Wrapped Expectations

Because errors will bubble up, it is possible to wrap other expectations in a SimpleMatcher.

  def be_even
    simple_matcher("an even number") { |given| (given % 2).should == 0 }
  end

BE VERY CAREFUL when you do this. Only use wrapped expectations for matchers that will always be used in only the positive (should) or negative (should_not), but not both. The reason is that is you wrap a should and call the wrapper with should_not, the correct result (the should failing), will fail when you want it to pass.

Given a Symbol argument, matches if the given 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)

[Validate]