[BEAM-3317] Use fixed system time for testing

[pawel-kaczmarczyk]

The problem here was caused by unfortunate timing during watermark retrieval. KinesisReader uses MovingFunction to decide if watermark should be advanced or not, parametrized with numSignificantBuckets=2 and numSignificantSamples=10. The test relied only on numSignificantSamples and did not take into consideration the time buckets. Now it sets the system time to a fixed value before execution so there will be no unfortunate time interatctions. I've also applied the same changes to other test that was likely to fail as it followed the same scheme.

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[pawel-kaczmarczyk]

@kennknowles @aromanenko-dev could you please take a look?

[aromanenko-dev]

@pawel-kaczmarczyk
For me, it seems reasonable to set fixed "system" time in tests, so LGTM.
The only one concern on my side - do you have an easy way how to reproduce initial issue to make sure that test will pass all the time?

[pawel-kaczmarczyk]

@aromanenko-dev It's enough to slow down the reader.advance() method that is called 10 times in the loop. I tested it by inserting a 1 second sleep inside this method and then the test failed every time.

[aromanenko-dev]

@pawel-kaczmarczyk Great, thanks!
@kennknowles Could you do review and merge if it's ok for you? Thank you

[kennknowles]

This is OK with me. I think even better would be to inject a clock into the reader (just pass to constructor) if it depends on such a service. I don't really know much about this connector, though, so it is just a vague suggestion.

[kennknowles]

Can you please squash the commits together? Then I will merge.

[pawel-kaczmarczyk]

@kennknowles commits squashed, thanks for your review!