Testing for expected failure

Questions & Help Questions
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7

My suggestion was not entirely right. You could write a expect_failure macro like this:

defmodule ExpectFailure do
  defmacro expect_failure(ast) do
    quote do
      try do
        unquote(ast)
        flunk("This should has crashed: " <> unquote(Macro.to_string(ast)))
      rescue
        e in ExUnit.AssertionError ->
          raise e

        _ ->
          :ok
      end
    end
  end
end

defmodule AsdfTest do
  use ExUnit.Case
  doctest Asdf
  import ExpectFailure

  def foo(x) when is_number(x) do
    x + 1
  end

  test "expect_failure catches errors" do
    expect_failure(foo("a"))
  end

  test "expect_failure should crash" do
    assert_raise ExUnit.AssertionError, fn ->
      expect_failure(foo(1))
    end
  end
end