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testresources: some examples

·3 mins

There’s been a clamor for more documentation on how to use testresources. While I’m not qualified to show you the best way to use it, I can show you the way that I would begin to use it.

The linked files are a bunch of unit tests for database code that uses Storm. Where a real test suite might use an in-memory database, this test suite uses on on-disk sqlite database to better illustrate testresources. This database needs to be removed and built again after each test to guarantee test isolation.

You’ll need testresources, Storm and testtools in your Python import path to run these examples.

The first file, complex-example.py, shows how I might do this without testresources. I create a DatabaseService class that has a setUp and tearDown of its own, and a get_store() method that tests are likely to use. This might not be the best thing for databases, but is very close to what I’d do for network services in tests, where I would need to start the service, stop it and have methods to get URLs, clients and other information about the service. If you run the file, you’ll see that the database is created at the start of each test, and destroyed before the test finishes. In total, it’s created and destroyed three times.

The second file, complex-example-2.py, shows how to switch to using testresources. To do this I,

  • added a TestResource subclass called DatabaseResource that implements make() and clean() by delegating to a DatabaseService.
  • changed the test case to subclass ResourcedTestCase
  • added ‘resources = [(‘database’, DatabaseResource())] as a class variable of the test case.

Instead of using DatabaseService() in the test, I could have, and perhaps should have, declared a module level instance of DatabaseResource. In that case, the code would have looked like:

class _DatabaseResource(TestResource):...DatabaseResource = _DatabaseResource()class TestPerson(unittest.TestPerson):...resources = [('database', DatabaseResource)]...

Running the file shows that the behaviour is the same as the first example: the database is created and destroyed in each test.

The third file, complex-example-3.py, shows how to take advantage of OptimisingTestSuite (sic). We load the test suite as usual, adsorb (sic) them into an OptimisingTestSuite and return that. We also have to explicity declare when a test dirties the DatabaseResource. I chose to do this by adding a dirtied() method to the DatabaseService. If I had used a singleton (as above), then I would have just called dirtied on that.

Anyway, if you run the third example, you’ll see that the database is created and destroyed outside the tests and that its only done twice. The test suite has been optimized by sharing resources between tests when possible.

I hope this helps explain how to use testresources. Certainly writing has been a useful exercise for me, it’s highlighted that:

  • a list of 2-tuples isn’t quite right for declaring which resources a test uses.
  • the dirtied API is inconvenient
  • TestResource remains a confusing name for the class, as it conflates the resource acquisition and cleanup with the actual resource.
  • Some of the API docs are wrong (notably the ones for ResourcedTestCase).
  • The pattern of “resource object with setUp, tearDown, dirtied (and addCleanup)” should perhaps be turned into Python code.

I long for your thoughts.

Examples:

complex-example.py
complex-example-2.py
complex-example-3.py

Update: Correct links to example Python files.

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