show-branch tests: modernize test code
Modernize test code added in ce567d1867a (Add test to show that show-branch misses out the 8th column, 2008-07-23) and 11ee57bc4c4 (sort_in_topological_order(): avoid setting a commit flag, 2008-07-23) to use test helpers. I'm renaming "out" to "actual" for consistency with other tests, and introducing a "branches.sorted" file in the setup, to make it clear that it's important that the list be sorted in this particular way. The "show-branch" output is indented with spaces, which would cause complaints under "git show --check" with an indented here-doc block. Let's prefix the lines with "> " to work around that, and to make it clear that the leading whitespace is important. We can also get rid of the hardcoding of "main" added here in 334afbc76fb (tests: mark tests relying on the current default for `init.defaultBranch`, 2020-11-18). For this test we're setting up an "initial" commit anyway, and now that we've moved over to test_commit we can reference that instead. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>