Some tweaks to simplify adding and running tests.
- Use test_tick for predictable, sort of realistic commit dates;
- Use test_cmp as "test_cmp expected actual" --- some crazy
content that was not expected should cause the test to fail;
- Remove and re-add all files at the start of each test so the
worktree is easier to think about;
- Avoid using cat where not necessary for clarity.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>