Errors in setUp can lead to misleading error messaging

[David Stanek]

It is possible to create a fixture that is hard to debug by overriding Fixture.setUp and not calling it *first* in the subclass' setUp implementation. The fixture instance is not in a usable state until after the parent setUp is called so any errors that happen before that are lost.

Example code:

    class MyFixture(fixtures.Fixture):

        def setUp(self):
            # do stuff that would raise an exception
            raise Exception
            super(MyFixture, self).setUp()

Error message:

    ======================================================================
    ERROR: test_test.TheTest.test
    ----------------------------------------------------------------------
    _StringException: Traceback (most recent call last):
      File "/tmp/testit/test_test.py", line 16, in setUp
        self.useFixture(MyFixture())
      File "/usr/local/lib/python2.7/dist-packages/testtools/testcase.py", line 611, in useFixture
        gather_details(fixture.getDetails(), self.getDetails())
      File "/usr/local/lib/python2.7/dist-packages/fixtures/fixture.py", line 148, in getDetails
        result = dict(self._details)
    AttributeError: 'MyFixture' object has no attribute '_details'

I didn't see this explicitly documented so it took me a little while to find the source of my errors. I think this would either be documented or possibly have Fixture._clear_cleanups called from within Fixture.__init__. I'd be happy to provide a patch for either solution, just let me know which one is more correct.

[Robert Collins (lifeless)]

This is a pure documentation issue IMO - doing it in __init__ would prevent fixture reuse.

[Robert Collins (lifeless)]

I think we've solved this with the new _setUp method, which doesn't require super() at all.