David Turner a127805b4a
[Zen2] Simulate scheduling delays (#34181)
Today we schedule tasks (both immediate and future ones) exactly when
requested. In fact it is more realistic to allow for a small amount of delay in
the scheduling of tasks, and this helps to exercise more interleavings of
actions and therefore to improve test coverage.

This change adds to the DeterministicTaskQueue the ability to add a random
delay to the scheduling of tasks.

This change also provides more explicit timeouts for stabilisation in the
CoordinatorTests.

Using the randomised scheduling feature in the CoordinatorTests also found a
situation in which we could become a leader, then a candidate, and then a
leader again very quickly, causing a clash of the _BECOME_MASTER_ and
_FINISH_ELECTION_ tasks. We change their behaviour to not consider these
duplicates to be problematic.
2018-10-02 11:22:05 +01:00
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