[PR] Refactor the FIELD pseudo-cause into the catch-all events and a field filter

[kopf-archiver]

A pull request by nolar at 2019-05-22 14:12:10+00:00
Original URL: zalando-incubator/kopf#69
Merged by nolar at 2019-05-28 15:36:27+00:00

Issue : #13

The FIELD pseudo-cause was introduced as an easy way to mark the per-field handlers (@kopf.on.field), and then to select them on the event handling. The field handlers were handled separately, after all the object handlers.

Over time, this pseudo-cause was merged into the overall handling routine, and has become a problem: it prevents further refactoring (of event/cause detection and handling), which in turn is needed for the test coverage.

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This PR is a set of changes extracted from a bigger branch for the ease of code review (one small part at a time). It does NOT change the behaviour of the framework or of any handlers; it just changes the internal implementation of it:

• No more FIELD pseudo-causes in the code.
• The catch-all handlers (event==None) with field property set are now used — i.e. any event as long as this field is in the diff. Efficiently, it means only the UPDATE events — same as before.

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In addition, the tests of handler selection were improved to reflect all cases; and to make the test ids more readable.