Merge branch 'fc/completion-test-simplification' into next

Merge branch 'fc/completion-test-simplification' into next

Clean up completion tests.  Use of conslidated helper may make
instrumenting one particular test during debugging of the test
itself, but that issue should be addressed in some other way
(e.g. making sure individual tests in 9902 can be skipped).

* fc/completion-test-simplification:
  completion: simplify __gitcomp() test helper
  completion: refactor __gitcomp related tests
  completion: consolidate test_completion*() tests
  completion: simplify tests using test_completion_long()
  completion: standardize final space marker in tests
  completion: add comment for test_completion()