       # File: assertion_test.exs
 
       # 1) Start ExUnit.
-      ExUnit.start
+      ExUnit.start()
 
       # 2) Create a new test module (test case) and use "ExUnit.Case".
       defmodule AssertionTest do


      * `:name` - the test name
      * `:module` - the test module
      * `:state` - the test error state (see ExUnit.state)
      * `:time` - the time to run the test
      * `:tags` - the test tags
      * `:logs` - the captured logs

  The minimum example of a `test_helper.exs` file would be:

      # test/test_helper.exs
      ExUnit.start()

  Mix will load the `test_helper.exs` file before executing the tests.
  It is not necessary to `require` the `test_helper.exs` file in your test
  files. See `Mix.Tasks.Test` for more information.
  """

  @typedoc "The error state returned by `ExUnit.Test` and `ExUnit.TestModule`"
  @type state :: nil | {:failed, failed} | {:skip, binary} | {:invalid, module}
  @type failed :: [{Exception.kind(), reason :: term, Exception.stacktrace()}]

  defmodule Test do
    @moduledoc """
