Add tests for Sync & Discover mode

[Phanatic]

Adds tests for the Sync and Discover mode in the CLI

=== RUN   TestSync_CanFilterSchema
--- PASS: TestSync_CanFilterSchema (0.00s)
=== RUN   TestSync_CanStartFromEmptyState
--- PASS: TestSync_CanStartFromEmptyState (0.00s)
=== RUN   TestSync_PrintsStreamSchema
--- PASS: TestSync_PrintsStreamSchema (0.00s)
=== RUN   TestSync_PrintsStreamState
--- PASS: TestSync_PrintsStreamState (0.00s)
=== RUN   TestSync_UsesStateIfIncrementalSyncRequested
--- PASS: TestSync_UsesStateIfIncrementalSyncRequested (0.00s)
=== RUN   TestSync_PrintsOldStateIfNoNewStateFound
--- PASS: TestSync_PrintsOldStateIfNoNewStateFound (0.00s)
=== RUN   TestSync_PrintsNewStateIfFound
--- PASS: TestSync_PrintsNewStateIfFound (0.00s)

=== RUN   TestDiscover_CanFailIfCredentialsInvalid
--- PASS: TestDiscover_CanFailIfCredentialsInvalid (0.00s)
=== RUN   TestDiscover_CanFailIfCannotQuery
--- PASS: TestDiscover_CanFailIfCannotQuery (0.00s)
=== RUN   TestDiscover_SchemaHasPrimaryKeys
--- PASS: TestDiscover_SchemaHasPrimaryKeys (0.00s)
=== RUN   TestDiscover_SchemaHasCursorProperties
--- PASS: TestDiscover_SchemaHasCursorProperties (0.00s)
=== RUN   TestDiscover_SchemaHasValidMetadata
--- PASS: TestDiscover_SchemaHasValidMetadata (0.00s)

[mdlayher]

Once you start to get into big nested comparisons like this, it gets easy to gloss over the details. It may be easier to compare a full "want" map versus the "got" result from GetPropertyMap so that the test libraries can spit out a nice diff of the whole thing rather than making assertions on each key/value pair.

[mdlayher]

This implies that it's possible for Read to return nil, nil above? Is that an expected behavior? Generally I'd expect some sort of sentinel value or error instead.