Allow controlling Timekeeper in tests for `sendAfter`

[bhamiltoncx]

Currently, Timekeeper only supports physical wall-clock time (it uses Date.now() and setInterval()), and there's no way to provide a fake version in tests.

Ideally, we'd have some way to provide the current time from outside in a test (Date.now()) as well as a way to control when callbacks passed to setInterval() fire.

Jest provides timer mocks which can help, but they require knowing the implementation of Timekeeper in order to function.

[bhamiltoncx]

Looks like not everything goes through Timekeeper:

https://github.com/search?q=repo%3Atimgit%2Fpg-boss+%2Fnow%5C%28%2F&type=code

There's also a bunch of logic in src/plans.ts which uses Postgres now(), most importantly fetchNextJob():

pg-boss/src/plans.ts

Line 674 in 87d69a0

!ignoreStartAfter ? 'start_after < now()' : '',

[timgit]

There are other test-specific configuration options used in the test suite which could an option to mock this, but you're right, it would be a bit more work to isolate the clock from SQL in plans

[bhamiltoncx]

Seems the typical mechanism is creating a schema override, defining a function overrride.now(), then prepending override to search_path.

https://gist.github.com/thehesiod/d0314d599c721216f075375c667e2d9a