Doctest for bad module with failure

We can add another test case that was reported to return bad results.

def fib(n):
    """
    Fibonacci sequence 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...

    >>> fib(1)
    0

    >>> fib(7)
    8

    >>> fib(10)
    34

    >>> fib(42)
    165580141
    """
    fibs = [0, 1]
    for _ in range(n-2):
        fibs.append(fibs[-1] + fibs[-2])
    return fibs[-1]

We can run doctest:

$ python3 -m doctest fibonacci.py
**********************************************************************
File "src/examples/testing/failure/fibonacci.py", line 5, in fibonacci.fib
Failed example:
    fib(1)
Expected:
    0
Got:
    1
**********************************************************************
1 item had failures:
   1 of   4 in fibonacci.fib
***Test Failed*** 1 failure.

It still checked all the 4 test cases and reported that one of them failed.

The exit code will also indicate the failure.

Exit code on Linux and macOS:

$ echo $?
1

Exit code on Windows:

> echo %ERRORLEVEL%
1

At this point we probably need to fix our code, but for this course we are more interested in the various ways we can test code and how failures are reported.