ApprovalTests.Python

Capturing Human Intelligence - ApprovalTests is an open source assertion/verification library to aid testing.
approvaltests is the ApprovalTests port for Python.

For more information see: www.approvaltests.com.

What can I use ApprovalTests for?

You can use ApprovalTests to verify objects that require more than a simple assert including long strings, large arrays, and complex hash structures and objects. ApprovalTests really shines when you need a more granular look at the test failure. Sometimes, trying to find a small difference in a long string printed to STDOUT is just too hard!
ApprovalTests solves this problem by providing reporters which let you view the test results in one of many popular diff utilities.

SETUP

From pypi:

pip install approvaltests

GETTING STARTED

Example using pytest:

from approvaltests.approvals import verify    

def test_simple(self):
    result = "foobar"
    verify(result)

Install the plugin pytest-approvaltests and use it to select a reporter:

pip install pytest-approvaltests
pytest --approvaltests-use-reporter='PythonNative'

Approvals work by comparing the test results to a golden master. If no golden master exists you can create a snapshot of the current test results and use that as the golden master. The reporter helps you manage the golden master.
Whenever your current results differ from the golden master, the reporter will launch an external application and then change some part of the system. Either you will update the master because you expected the changes and they are good, or you will go back to your code and update or roll back your changes to get your results back in line with the golden master.

The reporter is used both to alert you to changes in your test output, and to provide a tool to update the golden master. In this snippet, we chose the 'PythonNative' reporter when we ran the tests. For more information about selecting reporters see the documentation

Example using unittest:

import unittest

from approvaltests.approvals import verify
from approvaltests.reporters.generic_diff_reporter_factory import GenericDiffReporterFactory
    
    
class GettingStartedTest(unittest.TestCase):
    def setUp(self):
        self.reporter = GenericDiffReporterFactory().get_first_working()

    def test_simple(self):
        verify('Hello', self.reporter)


if __name__ == "__main__":
    unittest.main()

This example is similar to the pytest version shown above, except we are selecting the reporter in the test code rather than at runtime. ApprovalTests.Python come with a few reporters configured, supporting Linux, Mac OSX, and Windows. In the example shown above, we use the GenericDiffReporterFactory to find and select the first diff utility that exists on our system. Later, we pass that reporter to the verify method so that it can be used if the test fails.

You don't have to do it this way. You can request a specific reporter from the factory using the get method

class GettingStartedTest(unittest.TestCase):
    def setUp(self):
        self.factory = GenericDiffReporterFactory()

    def test_simple(self):
        verify('Hello', self.factory.get('BeyondCompare4'))

Or you can build your own GenericDiffReporter on the fly

class GettingStartedTest(unittest.TestCase):
    def test_simple(self):
        verify('Hello', GenericDiffReporter(('Custom', 'C:/my/favorite/diff/utility.exe')))

As long as C:/my/favorite/diff/utility.exe can be invoked from the command line using the format utility.exe file1 file2 then it will be compatible with GenericDiffReporter. Otherwise you will have to derive your own reporter, which we won't cover here.

To wrap things up, I should note that you can completely replace the collection of reporters known to the reporter factory by writing your own JSON file and loading it.

For example if you had C:/myreporters.json

[
    [
        "BeyondCompare4",
        "C:/Program Files (x86)/Beyond Compare 4/BCompare.exe"
    ],
    [
        "WinMerge",
        "C:/Program Files (x86)/WinMerge/WinMergeU.exe"
    ],
    [
        "Tortoise",
        "C:/Program Files (x86)/TortoiseSVN/bin/tortoisemerge.exe"
    ]
]

You could then use that file by loading it into the factory:

import unittest

from approvaltests.approvals import verify
from approvaltests.reporters.generic_diff_reporter_factory import GenericDiffReporterFactory


class GettingStartedTest(unittest.TestCase):
    def setUp(self):
        factory = GenericDiffReporterFactory()
        factory.load('C:/myreporters.json')
        self.reporter = factory.get_first_working()

    def test_simple(self):
        verify('Hello', self.reporter)

if __name__ == "__main__":
    unittest.main()

Of course, if you have some interesting new reporters in myreporters.json then please consider updating the reporters.json file that ships with Approvals and submitting a pull request.

SUPPORT AND DOCUMENTATION

Documentation
GitHub: https://github.com/approvals/ApprovalTests.Python
ApprovalTests Homepage: http://www.approvaltests.com

For developers

Pull requests are welcomed, particularly those accompanied by automated tests.

To run the self-tests, install pytest and tox, then execute

python3 -m tox

This will run the self-tests on several python versions. We would like to continue to support python 2.