It's very possible that without a red test, your green test would be green with inputs for which you intended it to be red. It's not enough to know that the te

It's very possible that without a red test, your green test would be green with inputs for which you intended it to be red. It's not enough to know that the test pass, you need to make sure the test would fail. Otherwise it's like having a cybernetic canary that doesn't need air to survive (great example, isn't it?).