This improves the unit tests for the repository form, supplying default

data (simplifying the data that has to be posted in each test) and

ensuring that we're always setting some data we would have already

expected to be set (for instance, setting visible=True).
The visible flag in particular was needed to perform repository

validation, which executes some code paths that are pretty important to

check. We weren't setting this before, so we weren't executing these

code paths, which impacted some in-progress work. This is now set, and

we're disabling the actual repository communication parts of the tests

through spies instead of an older validate_repository flag we're now

removing.

Unit tests passed.
Used this along with another upcoming change and found regressions that

the test suite previously did not uncover.