Merge branch 'fc/completion-test-simplification'

Clean up completion tests. Use of conslidated helper may make instrumenting one particular test during debugging of the test itself, but I think 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()