A Test::Unit runner that can run tests by line number.
Latest commit 9bcbf61 May 22, 2017 @zamith zamith Version 1.5.1



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

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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.

Gem::Specification.new do |gem|
  # ...
  gem.add_development_dependency "m", "~> 1.5.0"

m works on Ruby 2.0+ only.


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


m works with a few Ruby test frameworks:

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


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 TEST=test/minitest_5_test.rb

In the case of minitest 5, we have to specify the test to run, because running the whole suite will fail due to incompatibilities with ruby (at least until 2.1.1).


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