 
   @doc """
   API used to run the tests. It is invoked automatically
-  if ExUnit is started via `ExUnit.start`.
+  if ExUnit is started via `ExUnit.start/1`.
 
   Returns the number of failures.
   """

  ExUnit supports the following options:

  * `:color` - When color should be used by specific formatters.
               Defaults to the result of `IO.ANSI.terminal?`;

  * `:formatter` - The formatter that will print results.
                   Defaults to `ExUnit.CLIFormatter`;


      # File: assertion_test.exs

      # 1) Start ExUnit.
      ExUnit.start

      # 2) Create a new test module (test case) and use `ExUnit.Case`.
      defmodule AssertionTest do
        # 3) Notice we pass `async: true`, this runs the test case
        #    concurrently with other test cases
        use ExUnit.Case, async: true

        # 4) A test is a function whose name starts with
        #    `test` and receives a context.
        def test_always_pass(_) do
          assert true
        end

        # 5) Use the `test` macro instead of `def` for clarity.
        test "the truth" do
          assert true
        end
      end

  To run the tests above, run the file
  using `elixir` from the command line. Assuming you named the file
  `assertion_test.exs`, you can run it as:

      bin/elixir assertion_test.exs

  ## Case, Callbacks and Assertions

  See [`ExUnit.Case`](ExUnit.Case.html) and [`ExUnit.Callbacks`](ExUnit.Callbacks.html) for more information about
  defining test cases.

  The [`ExUnit.Assertions`](ExUnit.Assertions.html) module contains a set of macros to easily
  generate assertions with appropriate error messages.

  ## Integration with Mix

  Mix is the project management and build tool for Elixir. Invoking `mix test`
  from the command line will run the tests in each file matching the pattern
  `*_test.exs` found in the `test` directory of your project.

  You must create a `test_helper.exs` file inside the
  `test` directory and put the code common to all tests there.

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