[Dynamic Protocol State] Extend tests for EpochStateMachine

[durkmurder]

Context

Added a test which verifies that epoch transition indeed happens in edge cases described in #5631.

[AlexHentschel]

Thanks for the clean and well-documented test. Added a few minor suggestions for improving the tests specificity and documentation.

[AlexHentschel]

I feel that only looking the epoch phase is a relatively coarse check, that could succeed in a variety of ways despite the Epoch State machine doing something wrong. I may be overlooking something, but I feel it should be relatively straight forward to verify that we produce the expected epoch state here:

expectedEpochState := &flow.ProtocolStateEntry{
  PreviousEpoch:                   s.parentEpochState.CurrentEpoch.Copy(),
  CurrentEpoch:                    *s.parentEpochState.NextEpoch.Copy(),
  NextEpoch:                       nil,
  InvalidEpochTransitionAttempted: true,
}

and with that, we should be able to do

Suggested change

	s.epochStateDB.On("StoreTx", mocks.Anything, mocks.Anything).Run(func(args mocks.Arguments) {
	updatedState := args[1].(*flow.ProtocolStateEntry)
	require.Equal(s.T(), flow.EpochPhaseStaking, updatedState.EpochPhase())
	}).Return(storeTxDeferredUpdate.Execute, nil).Once()
	s.mutator.On("SetEpochStateID", mocks.Anything).Return().Once()
	s.epochStateDB.On("StoreTx", expectedEpochState.ID(), expectedEpochState).Return(storeTxDeferredUpdate.Execute, nil).Once()
	s.mutator.On("SetEpochStateID", expectedEpochState.ID()).Return().Once()

Hope that makes sense. 😅

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.51%. Comparing base (24ed447) to head (82127d8).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5681      +/-   ##
==========================================
- Coverage   55.52%   55.51%   -0.02%     
==========================================
  Files        1132     1132              
  Lines       89474    89474              
==========================================
- Hits        49680    49668      -12     
- Misses      35018    35033      +15     
+ Partials     4776     4773       -3     

Flag	Coverage Δ
unittests	55.51% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.