Implementing this test was quite a rabbithole, as in order to satisfy
backendTestBackendStates() the workspaces returned from
backend.Workspaces() must match exactly, and the shortcut taken to test
pagination in 3cc58813f0 created an
impossible circumstance that got plastered over with the fact that
prefix filtering is done clientside, not by the API as it should be.
Tagging does not rely on clientside filtering, and expects that the
request made to the TFC API returns exactly those workspaces with the
given tags.
These changes include a better way to test pagination, wherein we
actually create over a page worth of valid workspaces in the mock client
and implement a simplified pagination behavior to match how the TFC API
actually works.
1791b71196