def test_passes_on_unyielding_generator(self):
        """Test that assert_empty passes on an 'empty' generator."""
        def yield_nothing():
            if False:
                yield 0

        assertions.assert_empty(yield_nothing())

    def test_fails_on_infinite_generator(self):
        """Tests that assert_empty fails on an infinite generator."""
        def yes():
            while True:
                yield 'y'

        with assertions.assert_raises(AssertionError):
            assertions.assert_empty(yes())

    def test_max_elements_to_print_eq_0_means_no_sample_message(self):
        """Tests that when max_elements_to_print is 0, there is no sample in the error message."""
        iterable = [1, 2, 3]
        expected_message = "iterable %s was unexpectedly non-empty." % iterable

        def message_has_no_sample(exception):
            assertions.assert_equal(str(exception), expected_message)

        with assertions.assert_raises_such_that(
                AssertionError, message_has_no_sample):
            assertions.assert_empty(iterable, max_elements_to_print=0)

    def test_max_elements_to_print_eq_len_means_whole_iterable_sample_message(self):
        """
        Tests that when max_elements_to_print is equal to the length of
        the whole iterable, the whole iterable is printed.
        """
        elements = [1, 2, 3, 4, 5]
        iterable = (i for i in elements)
        expected_message = "iterable %s was unexpectedly non-empty. elements: %s" \
                         % (iterable, elements)

        def message_has_whole_iterable_sample(exception):
            assertions.assert_equal(str(exception), expected_message)

        with assertions.assert_raises_such_that(
                AssertionError, message_has_whole_iterable_sample):
            assertions.assert_empty(iterable, max_elements_to_print=len(elements))

    def test_max_elements_to_print_lt_len_means_partial_iterable_sample_message(self):
        """
        Tests that when max_elements_to_print is less than the length of the
        whole iterable, the first max_elements_to_print elements are printed.
        """
        elements = [1, 2, 3, 4, 5]
        iterable = (i for i in elements)
        max_elements_to_print = len(elements) - 1
        expected_message = "iterable %s was unexpectedly non-empty. first %i elements: %s" \
                         % (iterable, max_elements_to_print, elements[:max_elements_to_print])

        def message_has_whole_iterable_sample(exception):
            assertions.assert_equal(str(exception), expected_message)

        with assertions.assert_raises_such_that(
                AssertionError, message_has_whole_iterable_sample):
            assertions.assert_empty(iterable, max_elements_to_print=max_elements_to_print)

 def test_fails_on_nonempty_list(self):
     """Test that assert_empty fails on a nonempty list."""
     with assertions.assert_raises(AssertionError):
         assertions.assert_empty([0])

 def test_passes_on_empty_list(self):
     """Test that assert_empty passes on an empty list."""
     assertions.assert_empty([])

 def test_fails_on_nonempty_tuple(self):
     """Test that assert_empty fails on a nonempty tuple."""
     with assertions.assert_raises(AssertionError):
         assertions.assert_empty((0,))

 def test_passes_on_empty_tuple(self):
     """Test that assert_empty passes on an empty tuple."""
     assertions.assert_empty(())