Want to learn Minitest? Well, you came to the right place! But first, you’ll need to go clone minitest_playground So you can complete the YOUR TURN portions.

Foundational Information

Setup

• Install minitest from the command line with $ gem install minitest
• Files typically go in test dir.
• Common setup in test/test_helper.rb then you can require that at the top of any test file that needs the common setup

Writing Tests

• Put gem "minitest" before you require any minitest files to tell Ruby to use the gem we installed instead of the old version of Minitest that it shipped with.
• Load up and run minitest by requiring "minitest/autorun" (probably put this at the top of test_helper.rb)
• The default way to add a suite of tests is to make a class that inherits from Minitest::Test
• The default way to add a test to a suite is to define a method that begins with test_
• The default way to assert that code does what you want is assert(boolean_value)

Running Tests

Run tests from the command line by passing the name of the test file to ruby: $ ruby test/something_test.rb

Your Turn: Write Two Tests

Create a test suite named SimpleTest in test/simple_test.rb with two tests, one of which passes, the other fails. Run it with $ ruby test/simple_test.rb.

Test Order

You can reproduce the random order with the command line arguments --seed <value>, minitest tells you what seed it is using at the top of every run.

Your Turn: Intermittent Failure

Reproduce the intermittent failure in test/seed_test.rb

Running Certain Tests

• You can run a specific test with --name test_name
• You can run tests that match a regular expression with --name '/address/'

Your Turn: Filtering Tests

Filter the tests that run in test/filtering_test.rb

Test Instances

Each test method is invoked on a unique instance of the class (i.e. for each test method, instantiate the class and then invoke the method)

Your Turn: Instance Experiments

Prove to yourself that each test runs on its own instance in test/each_test_runs_in_its_own_instance_test.rb

Working with Support Code

Often you need support code. You could put it all in the test helper, but that would get big, and require every test that loads the helper to load that code, whether they need it or not (some code is expensive to load). A common pattern is to put it in a test/support/ directory.

Your Turn: Organizing Support Code

Move the support code from the test helper to the support dir and show that test/uses_support_test.rb still works

Skipping Tests

Some tests just aren’t ready yet, to bypass them, invoke the skip method

Your Turn: Adding Skips

Skip the unfinished feature in test/skip_test.rb

Capturing Standard Out

If you want to capture strings that were printed to standard output and standard error, you can run use capture_io

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out, err = capture_io do
  puts "hello"
  $stderr.puts "world"
end
out # => "hello\n"
err # => "world\n"

Your Turn: Capturing Output

Go capture the output from test/capture_output_test.rb

Nesting

Sometimes you want to a test suite within a test suite. For example, if I have several things I want to test about one method. The best way to do this is to define the inner test suite within the outer one, and then inherit from it.

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class ParentSuite < Minitest::Test

  # No tests in here, just helper methods
  def some_helper_method
    true
  end

  # Nested suite inherits from parent suite
  class NestedSuite < ParentSuite
    def test_something
      # I can call assertion helpers because I get them from ParentSuite
      # Which gets them from Minitest::Test
      # Which gets them from Minitest::Assertions
      #
      # And I can call the helper method because
      # I inherit from ParentSuite, where it is defined
      assert some_helper_method
    end
  end
end

Your Turn: Nested Tests

Go implement the nested test suites in test/nesting_test.rb

Asssertions

While the basic assert method is all you technically need, it’s not very descriptive or informative. There are a variety of more interesting and useful assertions.

Anything method asserting that a statement is truthful begins with assert_ and anything asserting that a statement is not truthful begins with refute_

Your Turn: Learning Assertions

There is a test suite around several of these in test/assertions_test.rb go update the methods to use the fancy assertions.