DataTableDiffTest: common objects as attributes
Move common objects as pre-configured class attributes
Mv setup helpers from DataTableDiffTest to DiffTestUtils
Mv DataRow test away from DataTableDiffTest
DataTableDiff - emit endTable summary event
diff/setEx/notifyListeners pattern in DiffBase
Encapsulate try/diff/setException/notifyListeners pattern in DiffBase.DiffRunner
inner class
rm return value from DataTableDiff.diff
Rely on emitted events instead