SynchronousDeferredRunTest does not use run_with_log_observers

[Tristan Seligmann]

I actually don't want to return a Deferred from my test at all, but I do want to use flush_logged_errors in my test.

[Robert Collins (lifeless)]

Would love a patch, do you need some pointers?

[Jonathan Lange (jml)]

https://github.com/testing-cabal/testtools/pull/171 will make this much easier, as it separates the logic out to a fixture.

After that lands, we can make a version of the fixture public, and then you'll have a much better way of flushing logged errors from SynchronousTestCase.