Avoid using context.Background in tests

[menghanl]

context.Background is used in many tests/benchmarks. Which might be misleading for users.

Some of the tests expect an error, so context.Background is probably OK.
We should check and make sure context.Background doesn't cause any problem.

[stale]

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[gauravgahlot]

@dfawley I would like to take this up.

[dfawley]

Sounds great, thank you!

I would do a grep for context.Background() in our tests (* - see below); any usages should appear in a context.WithTimeout or context.WithDeadline call as a rule. It's possible some tests add a timeout later, or a deadline isn't relevant for some tests, but I believe those should be rare.

* - find . -name '*_test.go' | xargs grep -F 'context.Background()'