Tests for walverine-based cites

[konklone]

I filed a ticket for walverine tests over at https://github.com/adelevie/walverine/issues/8 that links to CourtListener's own test suite.

One way to have both projects use the same set of tests would be to move these into an intermediate format appropriate for fixtures, as suggested by @tmcw in #76.

/cc @adelevie