Im my defense, I did test it. It was working for me.
But then someone else touched it without understanding it or flipped the truth value returned by one of the functions used by my code without properly fixing the call sites.
Edit: or they had a merge conflict and they don’t know how to correctly resolve those.
The first step of every testcase is supposed to fail to ensure a testing framework can fail in the scope of the testcase. In practice nobody acknowledges this, much less incorporates it.
Without, one is forced to concede that the test environment is not sane—and, therefore, no case under test is certifiable—because it cannot be known, for certain, if failure was a possibility.