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:
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.
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