Bacon – 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.

Whirl-wind tour

require 'bacon'

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

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

  it 'should have zero size' do
    @ary.size.should.equal 0 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

  # 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 palindrome

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

Now run it:

$ bacon 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 be a palindrome
- should have super powers [FAILED]

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

6 specifications (9 requirements), 1 failures, 0 errors

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

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

6 tests, 9 assertions, 1 failures, 0 errors

It also supports TAP:

$ bacon -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
not ok 6    - should have super powers: FAILED
# Bacon::Error: no super powers found
# 	./whirlwind.rb:39: A new array - should have super powers
# 	./whirlwind.rb:38
# 	./whirlwind.rb:3
# 6 tests, 9 assertions, 1 failures, 0 errors

$ bacon -p whirlwind.rb | taptap -q
Tests took 0.00 seconds.
FAILED tests 6
   6) should have super powers: FAILED

Failed 1/6 tests, 83.33% okay.

(taptap is available from

As of Bacon 1.1, it also supports Knock:

$ bacon -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
not ok - should have super powers: FAILED
# Bacon::Error: no super powers found
# 	./whirlwind.rb:39: A new array - should have super powers
# 	./whirlwind.rb:38
# 	./whirlwind.rb:3

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

(knock is available from

Implemented assertions

  • should.<predicate> and<predicate>

  • should.equal

  • should.match

  • /

  • 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.

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

context "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] shorter_than(5)

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

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/
-n, --name NAME          runs tests matching regexp NAME
-t, --testcase TESTCASE  runs tests in TestCases matching regexp TESTCASE

If you don’t want to use the standalone runner, run Bacon.summary_on_exit to install an exit handler showing the summary.


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

Bacon with autotest

Since version 1.0, there is autotest support. You need to tag your test directories (test/ or spec/) by creating an .bacon file there. Autotest then will find it. bin/bacon needs to be in PATH or RUBYPATH.

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

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.

  • December 21th, 2012: Fourth public release 1.2.0.

    • #satisfy will not pass arguments anymore to the block, use lexical scope.

    • Fixed Context#change?.

    • Add support for finding specs named like spec/*/_spec.rb.

    • Contexts nest properly.

    • Timer in TestUnitOutput.

    • Nested output for SpecDoxOutput.

    • Small cleanups and more tests.


Please mail bugs, suggestions and patches to <[email protected]>.

Git repository (patches rebased on HEAD are most welcome): git://


Copyright © 2007, 2008, 2012 Christian Neukirchen <>

Bacon is freely distributable under the terms of an MIT-style license. See COPYING or

Behavior-Driven Development






Christian Neukirchen