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m stands for metal, a better test/unit and minitest test runner that can run tests by line number.


Install via:

$ gem install m

If you’re using Bundler, you’ll need to include it in your Gemfile. Toss it into the test group:

group :test do
  gem 'm', '~> 1.5.0'

Developing a RubyGem? Add m as a development dependency. do |gem|
  # ...
  gem.add_development_dependency "m", "~> 1.5.0"

m works on Ruby 2.0+ only and support is only provided for versions currently maintained by the community.


Basically, I was sick of using the -n flag to grab one test to run. Instead, I prefer how RSpec’s test runner allows tests to be run by line number.

Given this file:

$ cat -n test/example_test.rb
 1  require 'test/unit'
 3  class ExampleTest < Test::Unit::TestCase
 4    def test_apple
 5      assert_equal 1, 1
 6    end
 8    def test_banana
 9      assert_equal 1, 1
10    end
11  end

You can run a test by line number, using format m TEST_FILE:LINE_NUMBER_OF_TEST:

$ m test/example_test.rb:4
Run options: -n /test_apple/

# Running tests:


Finished tests in 0.000525s, 1904.7619 tests/s, 1904.7619 assertions/s.

1 tests, 1 assertions, 0 failures, 0 errors, 0 skips

Hit the wrong line number? No problem, m helps you out:

$ m test/example_test.rb:2
No tests found on line 2. Valid tests to run:

 test_apple: m test/examples/test_unit_example_test.rb:4
test_banana: m test/examples/test_unit_example_test.rb:8

Want to run the whole test? Just leave off the line number.

$ m test/example_test.rb
Run options:

# Running tests:


Finished tests in 0.001293s, 1546.7904 tests/s, 3093.5808 assertions/s.

1 tests, 2 assertions, 0 failures, 0 errors, 0 skips

If you want to run all the tests in a directory as well as its subdirectories, use the -r flag:

$ m -r test/models
"Searching provided directory for tests recursively"
Run options:


Finished in 3.459902s, 45.0880 runs/s, 87.5747 assertions/s.

156 tests, 303 assertions, 0 failures, 0 errors, 13 skips

If you need to pass some option down to the actual runner, that is also supported:

$ m test/models -- --seed 1234
Run options: --seed 1234


Finished in 3.459902s, 45.0880 runs/s, 87.5747 assertions/s.

156 tests, 303 assertions, 0 failures, 0 errors, 13 skips

Ensure that you use the -- before the options, otherwise you'll get an invalid option error. Also, these extra option should always be the last argument.


m works with a few Ruby test frameworks:

  • Test::Unit
  • ActiveSupport::TestCase
  • MiniTest::Unit::TestCase
  • Minitest



This project uses Appraisal to test against different versions of dependencies.

To install all scenarios (appraisals):

bundle install
bundle exec appraisal install


You can run all the tests with:

bundle exec rake tests

You can also run tests selectively. For minitest 4 run:

appraisal minitest4 rake test

and the ones for minitest 5 with:

appraisal minitest5 rake test


This gem is MIT licensed, please see LICENSE for more information.