Fix flakiness of test_measure_sliding_window

[cpfair]

Proposed change

I noticed this test failure on #115146.

It appears that the async_block_till_done() call after inserting the entity states is not always sufficient to update the sensor values in time for the proceeding assertions. Removing the earlier (apparently redundant) call to async_block_till_done() seems to fix the issue.

I have no knowledge in the HA async architecture, but here's some speculation: Perhaps there are a cascade of tasks, some of which are not visible async_block_till_done, which continue executing beyond that synchronisation barrier. These could lead to nondeterministic results. By delaying the start of this hypothetical cascade of tasks until the test case's entity data is in place, there is no chance of stale state appearing later in the test.

This change appears to solve the flakiness in this particular test - but does not address any deeper root cause that may exist. It also does not attempt to identify and fix any other tests which may be suffering from this issue.

Before change: n=10,000 trials, 20 failures $\implies p_{fail} \ge 0.0008492$ with a 99% CI
After change: n=10,000 trials, 0 failures, $\alpha = (1 - 0.0008492)^{10,000} \approx 0.002 \le 0.01$ suggesting the flakiness is resolved

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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[bdraco]

Thanks @cpfair