Make sure the tests use mock maker with intended member accessor

[reta]

It seems like there is a gap in tests: the tests get mock maker instance (from environment setting) but not the member accessor it supposed to be used with. As such, the tests used reflection, not module accessor, all the time (see please #2834 (comment)).

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@TimvdLippe I could take it if you don't mind, thank you

[TimvdLippe]

Go ahead 👍