A small RSpec clone, with NSRunLoop powers
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MacBacon -- small RSpec clone.

"Truth will sooner come out from error than from confusion."
                                           ---Francis Bacon

Bacon is a small RSpec clone weighing less than 350 LoC but nevertheless providing all essential features.

This MacBacon fork is created and maintained by Eloy Durán (@alloy). It differs from regular Bacon in that it operates properly in a NSRunloop based environment. I.e. MacRuby/Objective-C. See the Objective-C runloop macros section for more info.

Whirl-wind tour

require 'mac_bacon'

describe 'A new array' do
  before do
    @ary = Array.new

  it 'should be empty' do
    @ary.should.not.include 1

  it 'should have zero size' do
    @ary.size.should.equal 0
    @ary.size.should.be.close 0.1, 0.5

  it 'should raise on trying fetch any index' do
    lambda { @ary.fetch 0 }.
      message.should.match(/out of array/)

    # Alternatively:
    should.raise(IndexError) { @ary.fetch 0 }

  it 'should have an object identity' do
    @ary.should.not.be.same_as Array.new

  it 'should perform a long running operation' do
    @ary.performSelector("addObject:", withObject:"soup", afterDelay:0.5)
    wait 0.6 do
      @ary.size.should.be 1

  # Custom assertions are trivial to do, they are lambdas returning a
  # boolean vale:
  palindrome = lambda { |obj| obj == obj.reverse }
  it 'should be a palindrome' do
    @ary.should.be.a palindrome

  it 'should have super powers' do
    should.flunk "no super powers found"

Now run it:

$ macbacon whirlwind.rb
A new array
  - should be empty
  - should have zero size
  - should raise on trying fetch any index
  - should have an object identity
  - should perform a long running operation
  - should be a palindrome
  - should have super powers [MISSING]

Bacon::Error: no super powers found
    ./whirlwind.rb:44:in `block': A new array - should have super powers

Bacon::Error: empty specification: A new array should have super powers

7 specifications (10 requirements), 1 failures, 0 errors

If you want shorter output, use the Test::Unit format:

$ macbacon -q whirlwind.rb
Bacon::Error: no super powers found
    ./whirlwind.rb:39: A new array - should have super powers

7 tests, 10 assertions, 1 failures, 0 errors

It also supports TAP:

$ macbacon -p whirlwind.rb
ok 1        - should be empty
ok 2        - should have zero size
ok 3        - should raise on trying fetch any index
ok 4        - should have an object identity
ok 5        - should be a palindrome
ok 6        - should perform a long running operation
not ok 7    - should have super powers: FAILED
# Bacon::Error: no super powers found
#   ./whirlwind.rb:44: A new array - should have super powers
# 7 tests, 10 assertions, 1 failures, 0 errors

$ macbacon -p whirlwind.rb | taptap -q
Tests took 0.00 seconds.
FAILED tests 7
   7) should have super powers: FAILED

Failed 1/7 tests, 83.33% okay.

(taptap is available from http://chneukirchen.org/repos/taptap/)

As of Bacon 1.1, it also supports Knock:

$ macbacon -k whirlwind.rb
ok - should be empty
ok - should have zero size
ok - should raise on trying fetch any index
ok - should have an object identity
ok - should be a palindrome
ok - should perform a long running operation
not ok - should have super powers: FAILED
# Bacon::Error: no super powers found
#   ./whirlwind.rb:4: A new array - should have super powers

$ bacon -k whirlwind.rb | kn-sum
7 tests, 1 failed (83.3333% succeeded)

(knock is available from http://github.com/chneukirchen/knock/)

Implemented assertions

  • should. and should.be.
  • should.equal
  • should.match
  • should.be.identical_to / should.be.same_as
  • should.raise(*exceptions) { }
  • should.change { }
  • should.throw(symbol) { }
  • should.satisfy { |object| }

Added core predicates

  • Object#true?
  • Object#false?
  • Proc#change?
  • Proc#raise?
  • Proc#throw?
  • Numeric#close?


before and after need to be defined before the first specification in a context and are run before and after each specification.

As of Bacon 1.1, before and after do nest in nested contexts.


You can use describe and context to make your tests clear and well organized.

context is alias of describe.

Shared contexts

You can define shared contexts in Bacon like this:

shared "an empty container" do
  it "should have size zero" do

  it "should be empty" do

describe "A new array" do
  behaves_like "an empty container"

These contexts are not executed on their own, but can be included with behaves_like in other contexts. You can use shared contexts to structure suites with many recurring specifications.


Custom matchers are simply lambdas returning a boolean value, for example:

def shorter_than(max_size)
  lambda { |obj| obj.size < max_size }

[1,2,3].should.be shorter_than(5)

You can use modules and extend to group matchers for use in multiple contexts.


When the -c, or --concurrency, option is passed to the macbacon command-line tool, than all specifications will be run concurrent through the use of Grand Central Dispatch.

Each specification runs in its own thread and gets its own runloop. In case you wat to perform certain specifications on the main thread (e.g. when dealing with views), you can specify that like so:

describe "Deals with the UI" do
  self.run_on_main_thread = true

  it "runs on the main thread" do
    # ...

Objective-C runloop macros

Often in Objective-C apps, code will not execute immediately, but scheduled on a runloop for later execution. Therefor a mechanism is provided that will postpone execution of blocks for a period of time.

(Note that using a block is imply syntactic sugar, you can call wait without a block too.)

All these macros may be used in before and after filters as well.

wait with fixed period of time

it 'should perform a long running operation' do
  # Here a method call is scheduled to be performed ~0.5 seconds in the future
  @ary.performSelector("addObject:", withObject:"soup", afterDelay:0.5)
  wait 0.6 do
    # This block is executed ~0.6 seconds in the future
    @ary.size.should.be 1

wait without fixed period of time, until resume is called

By default this usage of wait will wait for 10 seconds. If resume has not been called by that time, the spec fails.

def aDelegateCallbackMethod(sender)
  @delegateCallbackMethodCalled = true

it 'should wait until notified' do
  # Here a method is called that in the near future will result in the object calling back the delegate
  @object.delegate = self
  wait do
    # This block is executed once aDelegateCallbackMethod is called
    @delegateCallbackMethodCalled.should == true

If you want to specify the timeout, you can do that like so:

describe "specs that will wait for resume" do
  self.timeout = 20 # seconds

wait_for_change (Key-Value Observing)

This macro makes the specification an observer of the key path of the given object for the duration of the specification.

Like with wait without a fixed period, this usage of wait_for_change will by default wait for 10 seconds. If the KVO message has not arrived by that time, the spec fails.

class AKeyValueObservableClass
  attr_accessor :an_attribute

  def compute_an_attribute
    # trust me, this takes a few ms
    self.an_attribute = 'changed'

it 'should wait until AKeyValueObservableClass#an_attribute changes' do
  # Here a method is called that in the near future will update the 'an_attribute' value of the object
  wait_for_change observable, 'an_attribute' do
    # This block is executed once 'an_attribute' has changed value
    observable.an_attribute.should == 'changed'

Load NIBs

In case you have a NIB that defines the UI for the controller you're testing, then you can use the load_nib method to easily do so:

describe "PreferencesController" do
  before do
    @controller = PreferencesController.new
    nib_path = File.join(SRC_ROOT, 'app/views/PreferencesWindow.xib')
    @top_level_objects = load_nib(nib_path, @controller)

  # tests...


bacon standalone runner

-s, --specdox            do AgileDox-like output (default)
-q, --quiet              do Test::Unit-like non-verbose output
-p, --tap                do TAP (Test Anything Protocol) output
-k, --knock              do Knock output
-o, --output FORMAT      do FORMAT (SpecDox/TestUnit/Tap) output
-Q, --no-backtrace       don't print backtraces
-a, --automatic          gather tests from ./test/, include ./lib/
-c, --concurrent         runs multiple specs concurrently on multiple GCD threads
-n, --name NAME          runs tests matching regexp NAME
-t, --testcase TESTCASE  runs tests in TestCases matching regexp TESTCASE


You can use Object#should outside of contexts, where the result of assertion will be returned as a boolean. This is nice for demonstrations, quick checks and doctest tests.

>> require 'mac_bacon'
>> (1 + 1).should.equal 2
=> true
>> (6*9).should.equal 42
=> false

Converting specs

spec-converter is a simple tool to convert test-unit or dust style tests to test/spec specs.

It can be found at http://opensource.thinkrelevance.com/wiki/spec_converter.

Thanks to

  • Michael Fellinger, for fixing Bacon for 1.9 and various improvements.
  • Gabriele Renzi, for implementing Context#should.
  • James Tucker, for the autotest support.
  • Yossef Mendelssohn, for nested contexts.
  • everyone contributing bug fixes.


  • January 7, 2008: First public release 0.9.

  • July 6th, 2008: Second public release 1.0.

    • Add Context#should as a shortcut for Context#it('should ' + _).
    • describe now supports multiple arguments for better organization.
    • Empty specifications are now erroneous.
    • after-blocks run in the case of exceptions too.
    • Autotest support.
    • Bug fixes.
  • November 30th, 2008: Third public release 1.1.

    • Nested before/after.
    • Add -Q/--no-backtraces to not show details about failed specifications.
    • Add Knock output.
    • Bug fixes.
  • January 10th, 2011: MacBacon fork release 1.1

    • Make it work in a NSRunloop environment
    • Add wait
    • Remove extras, for now
  • March 12th, 2011: MacBacon fork release 1.3

    • Add NIB helper
    • exit with non-zero status when there were failures/errors
    • Add wait without explicit time
    • Add wait_for_change
  • TODO, 2012: MacBacon fork release 1.4

    • Use GCD to run specs concurrently when started with the -c or --concurrency command-line options.
    • Add delegate support, which notifies a delegate when a spec will start and once it finishes and also once Bacon has finished the run.
    • Simplified internals by removing callback/delegate system in favor of nested runloops.


Please mail bugs, suggestions and patches for Bacon to chneukirchen@gmail.com

Git repository (patches rebased on HEAD are most welcome): https://github.com/chneukirchen/bacon git://github.com/chneukirchen/bacon.git

For MacBacon contact eloy.de.enige@gmail.com

And repository location: https://github.com/alloy/MacBacon git://github.com/alloy/MacBacon.git


Copyright (C) 2007 - 2012 Christian Neukirchen http://purl.org/net/chneukirchen

Copyright (C) 2011 - 2012 Eloy Durán eloy.de.enige@gmail.com

Bacon is freely distributable under the terms of an MIT-style license. See COPYING or http://www.opensource.org/licenses/mit-license.php.