def test_keep_function_with_no_iterable():
operator = Keep()
with pytest.raises(TypeError):
operator.function(None, 1)
def test_keep_function_when_keeping_zero_values():
operator = Keep()
actual = operator.function([1, 2, 3], 0)
assert actual == []
def test_keep_function_with_invalid_iterable():
operator = Keep()
with pytest.raises(TypeError):
operator.function(1, 1)
def test_keep_function_when_keeping_more_values_than_exist():
operator = Keep()
actual = operator.function([1, 2, 3], 5)
assert actual == [1, 2, 3]