I have heard nice things about Minitest in the past, but have always worked with RSpec. Working on a small CLI utility recently, I wanted to minimize external dependencies, and since Minitest is built in to Ruby1 I thought I’d give it a shot.
Minitest allows you to run the tests directly from the command line. I started with this approach, test-driving a specific piece of logic I had in my head. Later I followed Bundler’s excellent documentation for writing a gem and adopted a Rakefile.
Spec or Unit Test Notation?
I started using the spec notation at first, but noticed that the error messages refer to auto-generated methods. Consider the following test:
require 'minitest/autorun' describe 'Foo' do it 'fails' do 1.must_equal 0 end end
Running it generates this output:
$ ruby foo_test.rb Run options: --seed 64703 # Running: F Failure: Foo#test_0001_fails [foo_test.rb:5]: Expected: 0 Actual: 1 ruby foo_test.rb:4 Finished in 0.001004s, 996.0157 runs/s, 996.0157 assertions/s. 1 runs, 1 assertions, 1 failures, 0 errors, 0 skips
That failure description references
Foo#test_0001_fails. I found this slightly disorienting even with a small amount of code, and it hinders navigating to the failing test by copying the method name from the error message and searching for it. I decided to switch to the regular unit test notation:
require 'minitest/autorun' class Foo < Minitest::Test def test_fails assert_equal 0, 1 end end
It reminds me of how I first learned unit testing, through JUnit examples2. The error report is clearer:
Failure: Foo#test_fails [foo_test.rb:5]: Expected: 0 Actual: 1
The notation also affects the assertion syntax.
Running Specific Tests
Once there were multiple test files, the need arose to run specific test files and specific tests on their own. A web search eventually led me to a post by Weston Ganger which provides the solution.
- Minitest documentation and source code
- How to create a Ruby gem with Bundler
- Minitest Quick Reference by Matt Sears
- Cheatsheet for Minitest at devhints.io
- A Few Ways To Run Your MiniTest Tests by Weston Ganger
Minitest started shipping with Ruby 1.9. The docs do mention, though, that not all gem functionality works with the built-in Minitest, so installing the gem might be best. ↩
I actually first encountered unit testing in Python, but reading Kent Beck’s Test-Driven Development: By Example really solidified things for me. I recommend this book to anyone starting out with unit testing. ↩