Yes, many of these tests should produce identical results under MyersDiff.  We should take your Diff abstraction idea and abstract both implementations, then do a common base test suite that provides most of these tests and use two subclasses to drive them for each implementation.

But a few of these, especially testEdit_NoUniqueMiddleSideA and B variants are specific to the current implementation of PatienceDiff not having a fallback.  MyersDiff shouldn't have the same results here.  And neither would a PatienceDiff that had an actual fallback for the degenerate case these represent.