pytest-regtest 0.15.0

pytest plugin for regression tests

pytest-regtest is a pytest-plugin for implementing regression tests. Compared to functional testing a regression test does not test if software produces correct results, instead a regression test checks if software behaves the same way as it did before introduced changes.

More about regression testing at https://en.wikipedia.org/wiki/Regression_testing. Regression testing is a common technique to get started when refactoring legacy code lacking a test suite.

pytest-regtest allows capturing selected output which then can be compared to the captured output from former runs.

To install and activate this plugin execute:

$ pip install pytest-regtest

pytest-regtest plugin provides a fixture named regtest which can be used as a file handle for recording data:

from __future__ import print_function

def test_squares_up_to_ten(regtest):

    result = [i*i for i in range(10)]

    # one way to record output:
    print(result, file=regtest)

    # alternative method to record output:
    regtest.write("done")

If you run this test script with pytest the first time there is no recorded output for this test function so far and thus the test will fail with a message including a diff:

$ py.test
...

def test_squares_up_to_ten(regtest):
E
>       Regression test failed
>
>       --- is
>       +++ tobe
>       @@ -1,2 +1 @@
>       -[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
>       -done
>       +

For accepting this output, we run pytest with the –regtest-reset flag:

$ py.test --regtest-reset

Now the next execution of py.test will succeed:

$ py.test

The recorded output was written to files in the subfolder _regtest_outputs next to your test script(s). You might keep this folder under version control.

Other features

Another way to record output is the regtest_redirect fixture:

def test_squares_up_to_ten(regtest_redirect):

    result = [i*i for i in range(10)]

    with regtest_redirect():
        print result

You can reset recorded output of files and functions individually as:

$ py.test --regtest-reset tests/test_00.py
$ py.test --regtest-reset tests/test_00.py::test_squares_up_to_ten

To supress the diff and only see the stats use:

$ py.test --regtest-nodiff

To see recorded output during test execution run:

$ py.test --regtest-tee -s

To support testing of the same code on different platforms by default pytest-regtest ignores differences in line breaks when comparing the approved to the actual output. To switch this off use the –regtest-regard-line-endings flag:

$ py.test --regtest-regard-line-endings