lib/rspec/matchers/aliased_matcher.rb
module RSpec
module Matchers
# Decorator that wraps a matcher and overrides `description`
# using the provided block in order to support an alias
# of a matcher. This is intended for use when composing
# matchers, so that you can use an expression like
# `include( a_value_within(0.1).of(3) )` rather than
# `include( be_within(0.1).of(3) )`, and have the corresponding
# description read naturally.
#
# @api private
class AliasedMatcher < MatcherDelegator
def initialize(base_matcher, description_block)
@description_block = description_block
super(base_matcher)
end
# Forward messages on to the wrapped matcher.
# Since many matchers provide a fluent interface
# (e.g. `a_value_within(0.1).of(3)`), we need to wrap
# the returned value if it responds to `description`,
# so that our override can be applied when it is eventually
# used.
def method_missing(*)
return_val = super
return return_val unless RSpec::Matchers.is_a_matcher?(return_val)
self.class.new(return_val, @description_block)
end
# Provides the description of the aliased matcher. Aliased matchers
# are designed to behave identically to the original matcher except
# for the description and failure messages. The description is different
# to reflect the aliased name.
#
# @api private
def description
@description_block.call(super)
end
# Provides the failure_message of the aliased matcher. Aliased matchers
# are designed to behave identically to the original matcher except
# for the description and failure messages. The failure_message is different
# to reflect the aliased name.
#
# @api private
def failure_message
@description_block.call(super)
end
# Provides the failure_message_when_negated of the aliased matcher. Aliased matchers
# are designed to behave identically to the original matcher except
# for the description and failure messages. The failure_message_when_negated is different
# to reflect the aliased name.
#
# @api private
def failure_message_when_negated
@description_block.call(super)
end
end
# Decorator used for matchers that have special implementations of
# operators like `==` and `===`.
# @private
class AliasedMatcherWithOperatorSupport < AliasedMatcher
# We undef these so that they get delegated via `method_missing`.
undef ==
undef ===
end
# @private
class AliasedNegatedMatcher < AliasedMatcher
def matches?(*args, &block)
if @base_matcher.respond_to?(:does_not_match?)
@base_matcher.does_not_match?(*args, &block)
else
!super
end
end
def does_not_match?(*args, &block)
@base_matcher.matches?(*args, &block)
end
def failure_message
optimal_failure_message(__method__, :failure_message_when_negated)
end
def failure_message_when_negated
optimal_failure_message(__method__, :failure_message)
end
private
DefaultFailureMessages = BuiltIn::BaseMatcher::DefaultFailureMessages
# For a matcher that uses the default failure messages, we prefer to
# use the override provided by the `description_block`, because it
# includes the phrasing that the user has expressed a preference for
# by going through the effort of defining a negated matcher.
#
# However, if the override didn't actually change anything, then we
# should return the opposite failure message instead -- the overriden
# message is going to be confusing if we return it as-is, as it represents
# the non-negated failure message for a negated match (or vice versa).
def optimal_failure_message(same, inverted)
if DefaultFailureMessages.has_default_failure_messages?(@base_matcher)
base_message = @base_matcher.__send__(same)
overriden = @description_block.call(base_message)
return overriden if overriden != base_message
end
@base_matcher.__send__(inverted)
end
end
end
end