How to run doc-tests without printing output

Question

I want to run doc-tests and get the number of failures, but not print any output. For example, I tried this:

    with open(os.devnull, 'w') as sys.stdout:
        tests_failed, tests_run = doctest.testmod(some_module,
                                                  optionflags=doctest.ELLIPSIS)

but this does not play nice with the test runner suite, which requires sys.stdout to write to a JSON file.

How can I run doc-tests without printing any output?

Answer 1

To capture (and thus silence) stdout, I use contextlib.redirect_stdout:

import io
import contextlib

[...]
    
    # in function running tests:
    f = io.StringIO()
    with contextlib.redirect_stdout(f):
       # run code that outputs stuff to stdout

    # stdout contents are now in f.get_value(), which you can use 
    # for further assertions, to output to a file, etc.

I did some experiments, to make sure this plays nice with doctest, and it seems to:

>>> f = io.StringIO()
>>> with contextlib.redirect_stdout(f):
...     doctest.testmod(my_project.utils)
...
>>> f.getvalue()
'TestResults(failed=0, attempted=10)\n'