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= minitest/{test,spec,mock,benchmark}

home :: bugs :: rdoc :: vim :: emacs::


minitest provides a complete suite of testing facilities supporting TDD, BDD, mocking, and benchmarking.

"I had a class with Jim Weirich on testing last week and we were
 allowed to choose our testing frameworks. Kirk Haines and I were
 paired up and we cracked open the code for a few test

 I MUST say that minitest is *very* readable / understandable
 compared to the 'other two' options we looked at. Nicely done and
 thank you for helping us keep our mental sanity."

-- Wayne E. Seguin

minitest/test is a small and incredibly fast unit testing framework. It provides a rich set of assertions to make your tests clean and readable.

minitest/spec is a functionally complete spec engine. It hooks onto minitest/test and seamlessly bridges test assertions over to spec expectations.

minitest/benchmark is an awesome way to assert the performance of your algorithms in a repeatable manner. Now you can assert that your newb co-worker doesn't replace your linear algorithm with an exponential one!

minitest/mock by Steven Baker, is a beautifully tiny mock (and stub) object framework.

minitest/pride shows pride in testing and adds coloring to your test output. I guess it is an example of how to write IO pipes too. :P

minitest/test is meant to have a clean implementation for language implementors that need a minimal set of methods to bootstrap a working test suite. For example, there is no magic involved for test-case discovery.

"Again, I can't praise enough the idea of a testing/specing
 framework that I can actually read in full in one sitting!"

-- Piotr Szotkowski

Comparing to rspec:

rspec is a testing DSL. minitest is ruby.

-- Adam Hawkins, "Bow Before MiniTest"

minitest doesn't reinvent anything that ruby already provides, like: classes, modules, inheritance, methods. This means you only have to learn ruby to use minitest and all of your regular OO practices like extract-method refactorings still apply.


  • minitest/autorun - the easy and explicit way to run all your tests.
  • minitest/test - a very fast, simple, and clean test system.
  • minitest/spec - a very fast, simple, and clean spec system.
  • minitest/mock - a simple and clean mock/stub system.
  • minitest/benchmark - an awesome way to assert your algorithm's performance.
  • minitest/pride - show your pride in testing!
  • Incredibly small and fast runner, but no bells and whistles.
  • Written by squishy human beings. Software can never be perfect. We will all eventually die.


See design_rationale.rb to see how specs and tests work in minitest.


Given that you'd like to test the following class:

class Meme def i_can_has_cheezburger? "OHAI!" end

def will_it_blend?


=== Unit tests

Define your tests as methods beginning with +test_+.

require "minitest/autorun"

class TestMeme < Minitest::Test def setup @meme = end

def test_that_kitty_can_eat
  assert_equal "OHAI!", @meme.i_can_has_cheezburger?

def test_that_it_will_not_blend
  refute_match /^no/i, @meme.will_it_blend?

def test_that_will_be_skipped
  skip "test this later"


=== Specs

require "minitest/autorun"

describe Meme do before do @meme = end

describe "when asked about cheeseburgers" do
  it "must respond positively" do
    _(@meme.i_can_has_cheezburger?).must_equal "OHAI!"

describe "when asked about blending possibilities" do
  it "won't say no" do
    _(@meme.will_it_blend?).wont_match /^no/i


For matchers support check out:

=== Benchmarks

Add benchmarks to your tests.

optionally run benchmarks, good for CI-only work!

require "minitest/benchmark" if ENV["BENCH"]

class TestMeme < Minitest::Benchmark # Override self.bench_range or default range is [1, 10, 100, 1_000, 10_000] def bench_my_algorithm assert_performance_linear 0.9999 do |n| # n is a range value @obj.my_algorithm(n) end end end

Or add them to your specs. If you make benchmarks optional, you'll need to wrap your benchmarks in a conditional since the methods won't be defined. In minitest 5, the describe name needs to match /Bench(mark)?$/.

describe "Meme Benchmark" do if ENV["BENCH"] then bench_performance_linear "my_algorithm", 0.9999 do |n| 100.times do @obj.my_algorithm(n) end end end end

outputs something like:

Running benchmarks:

TestBlah 100 1000 10000 bench_my_algorithm 0.006167 0.079279 0.786993 bench_other_algorithm 0.061679 0.792797 7.869932

Output is tab-delimited to make it easy to paste into a spreadsheet.

=== Mocks

Mocks and stubs defined using terminology by Fowler & Meszaros at

"Mocks are pre-programmed with expectations which form a specification of the calls they are expected to receive. They can throw an exception if they receive a call they don't expect and are checked during verification to ensure they got all the calls they were expecting."

class MemeAsker def initialize(meme) @meme = meme end

def ask(question)
  method =" ", "_") + "?"


require "minitest/autorun"

describe MemeAsker, :ask do describe "when passed an unpunctuated question" do it "should invoke the appropriate predicate method on the meme" do @meme = @meme_asker = @meme @meme.expect :will_it_blend?, :return_value

    @meme_asker.ask "will it blend"



==== Multi-threading and Mocks

Minitest mocks do not support multi-threading. If it works, fine, if it doesn't you can use regular ruby patterns and facilities like local variables. Here's an example of asserting that code inside a thread is run:

def test_called_inside_thread called = false pr = { called = true } thread = thread.join assert called, "proc not called" end

=== Stubs

Mocks and stubs are defined using terminology by Fowler & Meszaros at

"Stubs provide canned answers to calls made during the test".

Minitest's stub method overrides a single method for the duration of the block.

def test_stale_eh obj_under_test =

refute obj_under_test.stale?

Time.stub :now, do   # stub goes away once the block is done
  assert obj_under_test.stale?


A note on stubbing: In order to stub a method, the method must actually exist prior to stubbing. Use a singleton method to create a new non-existing method:

def obj_under_test.fake_method ... end

=== Running Your Tests

Ideally, you'll use a rake task to run your tests, either piecemeal or all at once. Both rake and rails ship with rake tasks for running your tests. BUT! You don't have to:

% ruby -Ilib:test test/minitest/test_minitest_test.rb
Run options: --seed 37685

# Running:

...................................................................... (etc)

Finished in 0.107130s, 1446.8403 runs/s, 2959.0217 assertions/s.

155 runs, 317 assertions, 0 failures, 0 errors, 0 skips

There are runtime options available, both from minitest itself, and also provided via plugins. To see them, simply run with +--help+:

% ruby -Ilib:test test/minitest/test_minitest_test.rb --help
minitest options:
    -h, --help                       Display this help.
    -s, --seed SEED                  Sets random seed. Also via env. Eg: SEED=n rake
    -v, --verbose                    Verbose. Show progress processing files.
    -n, --name PATTERN               Filter run on /regexp/ or string.
    -e, --exclude PATTERN            Exclude /regexp/ or string from run.

Known extensions: pride, autotest
    -p, --pride                      Pride. Show your testing pride!
    -a, --autotest                   Connect to autotest server.

You can set up a rake task to run all your tests by adding this to your Rakefile:

require "rake/testtask" do |t|
  t.libs << "test"
  t.libs << "lib"
  t.test_files = FileList["test/**/test_*.rb"]

task :default => :test

== Writing Extensions

To define a plugin, add a file named minitest/XXX_plugin.rb to your project/gem. That file must be discoverable via ruby's LOAD_PATH (via rubygems or otherwise). Minitest will find and require that file using Gem.find_files. It will then try to call +plugin_XXX_init+ during startup. The option processor will also try to call +plugin_XXX_options+ passing the OptionParser instance and the current options hash. This lets you register your own command-line options. Here's a totally bogus example:

# minitest/bogus_plugin.rb:

module Minitest
  def self.plugin_bogus_options(opts, options)
    opts.on "--myci", "Report results to my CI" do
      options[:myci] = true
      options[:myci_addr] = get_myci_addr
      options[:myci_port] = get_myci_port

  def self.plugin_bogus_init(options)
    self.reporter << if options[:myci]

=== Adding custom reporters

Minitest uses composite reporter to output test results using multiple reporter instances. You can add new reporters to the composite during the init_plugins phase. As we saw in +plugin_bogus_init+ above, you simply add your reporter instance to the composite via <<.

+AbstractReporter+ defines the API for reporters. You may subclass it and override any method you want to achieve your desired behavior.

start :: Called when the run has started. record :: Called for each result, passed or otherwise. report :: Called at the end of the run. passed? :: Called to see if you detected any problems.

Using our example above, here is how we might implement MyCI:

# minitest/bogus_plugin.rb

module Minitest
  class MyCI < AbstractReporter
    attr_accessor :results, :addr, :port

    def initialize options
      self.results = []
      self.addr = options[:myci_addr]
      self.port = options[:myci_port]

    def record result
      self.results << result

    def report
      CI.connect(addr, port).send_results self.results

  # code from above...

== FAQ

=== How to test SimpleDelegates?

The following implementation and test:

class Worker < SimpleDelegator
  def work

describe Worker do
  before do
    @worker =

  it "must respond to work" do
    _(@worker).must_respond_to :work

outputs a failure:

  1) Failure:
Worker#test_0001_must respond to work [bug11.rb:16]:
Expected #<Object:0x007f9e7184f0a0> (Object) to respond to #work.

Worker is a SimpleDelegate which in 1.9+ is a subclass of BasicObject. Expectations are put on Object (one level down) so the Worker (SimpleDelegate) hits +method_missing+ and delegates down to the instance. That object doesn't respond to work so the test fails.

You can bypass SimpleDelegate#method_missing by extending the worker with Minitest::Expectations. You can either do that in your setup at the instance level, like:

before do
  @worker =
  @worker.extend Minitest::Expectations

or you can extend the Worker class (within the test file!), like:

class Worker
  include ::Minitest::Expectations

=== How to share code across test classes?

Use a module. That's exactly what they're for:

module UsefulStuff
  def useful_method
    # ...

describe Blah do
  include UsefulStuff

  def test_whatever
    # useful_method available here

Remember, +describe+ simply creates test classes. It's just ruby at the end of the day and all your normal Good Ruby Rules (tm) apply. If you want to extend your test using setup/teardown via a module, just make sure you ALWAYS call super. before/after automatically call super for you, so make sure you don't do it twice.

=== How to run code before a group of tests?

Use a constant with begin...end like this:

describe Blah do SETUP = begin # ... this runs once when describe Blah starts end # ... end

This can be useful for expensive initializations or sharing state. Remember, this is just ruby code, so you need to make sure this technique and sharing state doesn't interfere with your tests.

=== Why am I seeing uninitialized constant MiniTest::Test (NameError)?

Are you running the test with Bundler (e.g. via bundle exec )? If so, in order to require minitest, you must first add the gem 'minitest' to your Gemfile and run +bundle+. Once it's installed, you should be able to require minitest and run your tests.

== Prominent Projects using Minitest:

  • arel
  • journey
  • mime-types
  • nokogiri
  • rails (active_support et al)
  • rake
  • rdoc
  • ...and of course, everything from seattle.rb...

== Developing Minitest:

Minitest requires {Hoe}[].

=== Minitest's own tests require UTF-8 external encoding.

This is a common problem in Windows, where the default external Encoding is often CP850, but can affect any platform. Minitest can run test suites using any Encoding, but to run Minitest's own tests you must have a default external Encoding of UTF-8.

If your encoding is wrong, you'll see errors like:

--- expected
+++ actual
@@ -1,2 +1,3 @@
 # encoding: UTF-8
 -"Expected /\\w+/ to not match \"blah blah blah\"."
 +"Expected /\\w+/ to not match # encoding: UTF-8
 +\"blah blah blah\"."

To check your current encoding, run:

ruby -e 'puts Encoding.default_external'

If your output is something other than UTF-8, you can set the RUBYOPTS env variable to a value of '-Eutf-8'. Something like:

RUBYOPT='-Eutf-8' ruby -e 'puts Encoding.default_external'

Check your OS/shell documentation for the precise syntax (the above will not work on a basic Windows CMD prompt, look for the SET command). Once you've got it successfully outputing UTF-8, use the same setting when running rake in Minitest.

=== Minitest's own tests require GNU (or similar) diff.

This is also a problem primarily affecting Windows developers. PowerShell has a command called diff, but it is not suitable for use with Minitest.

If you see failures like either of these, you are probably missing diff tool:

  4) Failure:
TestMinitestUnitTestCase#test_assert_equal_different_long [D:/ruby/seattlerb/minitest/test/minitest/test_minitest_test.rb:936]:
Expected: "--- expected\n+++ actual\[email protected]@ -1 +1 @@\n-\"hahahahahahahahahahahahahahahahahahahaha\"\n+\"blahblahblahblahblahblahblahblahblahblah\"\n"
  Actual: "Expected: \"hahahahahahahahahahahahahahahahahahahaha\"\n  Actual: \"blahblahblahblahblahblahblahblahblahblah\""

  5) Failure:
TestMinitestUnitTestCase#test_assert_equal_different_collection_hash_hex_invisible [D:/ruby/seattlerb/minitest/test/minitest/test_minitest_test.rb:845]:
Expected: "No visible difference in the Hash#inspect output.\nYou should look at the implementation of #== on Hash or its members.\n
  Actual: "Expected: {1=>#<Object:0x00000003ba0470>}\n  Actual: {1=>#<Object:0x00000003ba0448>}"

If you use Cygwin or MSYS2 or similar there are packages that include a GNU diff for Windows. If you don't, you can download GNU diffutils from (make sure to add it to your PATH).

You can make sure it's installed and path is configured properly with:

diff.exe -v

There are multiple lines of output, the first should be something like:

diff (GNU diffutils) 2.8.1

If you are using PowerShell make sure you run diff.exe, not just diff, which will invoke the PowerShell built in function.

== Known Extensions:

capybara_minitest_spec :: Bridge between Capybara RSpec matchers and Minitest::Spec expectations (e.g. page.must_have_content("Title")). color_pound_spec_reporter :: Test names print Ruby Object types in color with your Minitest Spec style tests. minispec-metadata :: Metadata for describe/it blocks & CLI tag filter. E.g. it "requires JS driver", js: true do & ruby test.rb --tag js runs tests tagged :js. minispec-rails :: Minimal support to use Spec style in Rails 5+. mini-apivore :: for swagger based automated API testing. minitest-around :: Around block for minitest. An alternative to setup/teardown dance. minitest-assert_errors :: Adds Minitest assertions to test for errors raised or not raised by Minitest itself. minitest-autotest :: autotest is a continuous testing facility meant to be used during development. minitest-bacon :: minitest-bacon extends minitest with bacon-like functionality. minitest-bang :: Adds support for RSpec-style let! to immediately invoke let statements before each test. minitest-bisect :: Helps you isolate and debug random test failures. minitest-blink1_reporter :: Display test results with a Blink1. minitest-capistrano :: Assertions and expectations for testing Capistrano recipes. minitest-capybara :: Capybara matchers support for minitest unit and spec. minitest-chef-handler :: Run Minitest suites as Chef report handlers minitest-ci :: CI reporter plugin for Minitest. minitest-context :: Defines contexts for code reuse in Minitest specs that share common expectations. minitest-debugger :: Wraps assert so failed assertions drop into the ruby debugger. minitest-display :: Patches Minitest to allow for an easily configurable output. minitest-documentation :: Minimal documentation format inspired by rspec's. minitest-doc_reporter :: Detailed output inspired by rspec's documentation format. minitest-emoji :: Print out emoji for your test passes, fails, and skips. minitest-english :: Semantically symmetric aliases for assertions and expectations. minitest-excludes :: Clean API for excluding certain tests you don't want to run under certain conditions. minitest-fail-fast :: Reimplements RSpec's "fail fast" feature minitest-filecontent :: Support unit tests with expectation results in files. Differing results will be stored again in files. minitest-filesystem :: Adds assertion and expectation to help testing filesystem contents. minitest-firemock :: Makes your Minitest mocks more resilient. minitest-focus :: Focus on one test at a time. minitest-gcstats :: A minitest plugin that adds a report of the top tests by number of objects allocated. minitest-global_expectations:: Support minitest expectation methods for all objects minitest-great_expectations :: Generally useful additions to minitest's assertions and expectations. minitest-growl :: Test notifier for minitest via growl. minitest-happy :: GLOBALLY ACTIVATE MINITEST PRIDE! RAWR! minitest-have_tag :: Adds Minitest assertions to test for the existence of HTML tags, including contents, within a provided string. minitest-hooks :: Around and before_all/after_all/around_all hooks minitest-hyper :: Pretty, single-page HTML reports for your Minitest runs minitest-implicit-subject :: Implicit declaration of the test subject. minitest-instrument :: Instrument ActiveSupport::Notifications when test method is executed. minitest-instrument-db :: Store information about speed of test execution provided by minitest-instrument in database. minitest-junit :: JUnit-style XML reporter for minitest. minitest-keyword :: Use Minitest assertions with keyword arguments. minitest-libnotify :: Test notifier for minitest via libnotify. minitest-line :: Run test at line number. minitest-logger :: Define assert_log and enable minitest to test log messages. Supports Logger and Log4r::Logger. minitest-macruby :: Provides extensions to minitest for macruby UI testing. minitest-matchers :: Adds support for RSpec-style matchers to minitest. minitest-matchers_vaccine :: Adds assertions that adhere to the matcher spec, but without any expectation infections. minitest-metadata :: Annotate tests with metadata (key-value). minitest-mock_expectations :: Provides method call assertions for minitest. minitest-mongoid :: Mongoid assertion matchers for Minitest. minitest-must_not :: Provides must_not as an alias for wont in Minitest. minitest-optional_retry :: Automatically retry failed test to help with flakiness. minitest-osx :: Reporter for the Mac OS X notification center. minitest-parallel_fork :: Fork-based parallelization minitest-parallel-db :: Run tests in parallel with a single database. minitest-power_assert :: PowerAssert for Minitest. minitest-predicates :: Adds support for .predicate? methods. minitest-profile :: List the 10 slowest tests in your suite. minitest-rails :: Minitest integration for Rails 3.x. minitest-rails-capybara :: Capybara integration for Minitest::Rails. minitest-reporters :: Create customizable Minitest output formats. minitest-rg :: Colored red/green output for Minitest. minitest-rspec_mocks :: Use RSpec Mocks with Minitest. minitest-server :: minitest-server provides a client/server setup with your minitest process, allowing your test run to send its results directly to a handler. minitest-sequel :: Minitest assertions to speed-up development and testing of Ruby Sequel database setups. minitest-shared_description :: Support for shared specs and shared spec subclasses minitest-should_syntax :: RSpec-style x.should == y assertions for Minitest. minitest-shouldify :: Adding all manner of shoulds to Minitest (bad idea) minitest-snail :: Print a list of tests that take too long minitest-spec-context :: Provides rspec-ish context method to Minitest::Spec. minitest-spec-expect :: Expect syntax for Minitest::Spec (e.g. expect(sequences).to_include :celery_man). minitest-spec-magic :: Minitest::Spec extensions for Rails and beyond. minitest-spec-rails :: Drop in Minitest::Spec superclass for ActiveSupport::TestCase. minitest-sprint :: Runs (Get it? It's fast!) your tests and makes it easier to rerun individual failures. minitest-stately :: Find leaking state between tests minitest-stub_any_instance :: Stub any instance of a method on the given class for the duration of a block. minitest-stub-const :: Stub constants for the duration of a block. minitest-tags :: Add tags for minitest. minitest-unordered :: Adds a new assertion to minitest for checking the contents of a collection, ignoring element order. minitest-vcr :: Automatic cassette managment with Minitest::Spec and VCR. minitest_log :: Adds structured logging, data explication, and verdicts. minitest_owrapper :: Get tests results as a TestResult object. minitest_should :: Shoulda style syntax for minitest test::unit. minitest_tu_shim :: Bridges between test/unit and minitest. mongoid-minitest :: Minitest matchers for Mongoid. mutant-minitest :: Minitest integration for mutant. pry-rescue :: A pry plugin w/ minitest support. See pry-rescue/minitest.rb. rspec2minitest :: Easily translate any RSpec matchers to Minitest assertions and expectations.

== Unknown Extensions:

Authors... Please send me a pull request with a description of your minitest extension.

  • assay-minitest
  • detroit-minitest
  • em-minitest-spec
  • flexmock-minitest
  • guard-minitest
  • guard-minitest-decisiv
  • minitest-activemodel
  • minitest-ar-assertions
  • minitest-capybara-unit
  • minitest-colorer
  • minitest-deluxe
  • minitest-extra-assertions
  • minitest-rails-shoulda
  • minitest-spec
  • minitest-spec-should
  • minitest-sugar
  • spork-minitest

== Minitest related goods


  • Ruby 2.3+. No magic is involved. I hope.


sudo gem install minitest

On 1.9, you already have it. To get newer candy you can still install the gem, and then requiring "minitest/autorun" should automatically pull it in. If not, you'll need to do it yourself:

gem "minitest" # ensures you"re using the gem, and not the built-in MT require "minitest/autorun"

... usual testing stuffs ...

DO NOTE: There is a serious problem with the way that ruby 1.9/2.0 packages their own gems. They install a gem specification file, but don't install the gem contents in the gem path. This messes up Gem.find_files and many other things (gem which, gem contents, etc).

Just install minitest as a gem for real and you'll be happier.


(The MIT License)

Copyright (c) Ryan Davis, seattle.rb

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.


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