module ActiveSupport::Testing::Deprecation

def assert_deprecated(match = nil, deprecator = nil, &block)

end
ActiveSupport::Deprecation.warn "foo should no longer be used"
assert_deprecated do

If no +deprecator+ is given, defaults to ActiveSupport::Deprecation.

end
CustomDeprecator.warn "foo should no longer be used"
assert_deprecated(nil, CustomDeprecator) do

If the +match+ is omitted (or explicitly +nil+), any deprecation warning will match.

end
CustomDeprecator.warn "foo should no longer be used"
assert_deprecated('foo', CustomDeprecator) do

The +match+ object may be a +Regexp+, or +String+ appearing in the message.

end
CustomDeprecator.warn "foo should no longer be used"
assert_deprecated(/foo/, CustomDeprecator) do

Asserts that a matching deprecation warning was emitted by the given deprecator during the execution of the yielded block. 
def assert_deprecated(match = nil, deprecator = nil, &block)
  result, warnings = collect_deprecations(deprecator, &block)
  assert !warnings.empty?, "Expected a deprecation warning within the block but received none"
  if match
    match = Regexp.new(Regexp.escape(match)) unless match.is_a?(Regexp)
    assert warnings.any? { |w| match.match?(w) }, "No deprecation warning matched #{match}: #{warnings.join(', ')}"
  end
  result
end

def assert_not_deprecated(deprecator = nil, &block)

end
CustomDeprecator.warn "message" # passes assertion
assert_not_deprecated do

end
ActiveSupport::Deprecation.warn "message" # fails assertion
assert_not_deprecated do

If no +deprecator+ is given, defaults to ActiveSupport::Deprecation.

end
CustomDeprecator.warn "message" # fails assertion
assert_not_deprecated(CustomDeprecator) do

Asserts that no deprecation warnings are emitted by the given deprecator during the execution of the yielded block. 
def assert_not_deprecated(deprecator = nil, &block)
  result, deprecations = collect_deprecations(deprecator, &block)
  assert deprecations.empty?, "Expected no deprecation warning within the block but received #{deprecations.size}: \n  #{deprecations * "\n  "}"
  result
end

def collect_deprecations(deprecator = nil)

end # => ["message"]
ActiveSupport::Deprecation.warn "message"
CustomDeprecator.warn "custom message"
collect_deprecations do

If no +deprecator+ is given, defaults to ActiveSupport::Deprecation.

end # => ["message"]
CustomDeprecator.warn "message"
collect_deprecations(CustomDeprecator) do

+deprecator+ during the execution of the yielded block.
Returns an array of all the deprecation warnings emitted by the given 
def collect_deprecations(deprecator = nil)
  deprecator ||= ActiveSupport::Deprecation
  old_behavior = deprecator.behavior
  deprecations = []
  deprecator.behavior = Proc.new do |message, callstack|
    deprecations << message
  end
  result = yield
  [result, deprecations]
ensure
  deprecator.behavior = old_behavior
end