t4254: modernize tests
- Don't start tests with 'test $? = 0' to catch preparation done
outside the test_expect_success block.
- Move writing the bogus patch and the expected output into the
appropriate test_expect_success blocks.
- Use the test_must_fail helper instead of manually checking for
non-zero exit code.
- Use the debug-friendly test_path_is_file helper instead of 'test -f'.
- No space after '>'.
Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>