The docstring will look like text you would see in a Python shell (including a prompt). Rig one of the tests to fail, just to see what will happen:

"""
Test for the factorial of 3 that should pass.
>>> factorial(3)
6
Test for the factorial of 0 that should fail.
>>> factorial(0)
1
"""

Write the following line of NumPy code:

return np.arange(1, n+1).cumprod()[-1]

We want this code to fail from time to time for demonstration purposes.

Run the doctest by calling the rundocs() function of the numpy.testing module, for instance, in the Python shell:

>>> from numpy.testing import rundocs
>>> rundocs('docstringtest.py')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "…/numpy/testing/utils.py", line 998,...