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py.test plugin for regression tests

Project description

This pytest-plugin allows capturing of output of test functions which can be compared to the captured output from former runs. This is a common technique to start TDD if you have to refactor legacy code which ships without tests.

To install and activate this plugin you have to run:

$ pip install pytest-regtest

from your command line.

This py.test plugin provides a fixture named regtest for recording data by writing to this fixture, which behaves like an output stream:

def test_squares_up_to_ten(regtest):

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

    # one way to record output:
    print >> regtest, result

    # alternative method to record output:

We can redirect stdout to this stream using 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

For recording the approved output, you run py.test with the –reset-regtest flag:

$ py.test --regtest-reset

The recorded output is written to text files in the subfolder _regtest_outputs next to your test scripts.

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

$ py.test --regtest-reset tests/
$ py.test --regtest-reset tests/

If you want to check that the testing function still produces the same output, you ommit the flag and run you tests as usual:

$ py.test

This shows diffs for the tests failing because the current and recorded output deviate.

To supress the diff and only see the stats use:

$ py.test --regtest-nodiff

If you want to see the recorded output on the commandline use:

$ py.test --regtest-tee -s

If you develop on mixed platforms it might be usefull to ignore white spaces at the end of the lines when comparing output. This can be achieved by specifying

$ py.test –regtest-ignore-line-endings

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