t5526: introduce test helper to assert on fetches
Tests in t/t5526-fetch-submodules.sh are unnecessarily noisy: * The tests have extra logic in order to reproduce the expected stderr literally, but not all of these details (e.g. the head of the remote-tracking branch before the fetch) are relevant to the test. * The expect.err file is constructed by the add_upstream_commit() helper as input into test_cmp, but most tests fetch a different combination of repos from expect.err. This results in noisy tests that modify parts of that expect.err to generate the expected output. To address both of these issues, introduce a verify_fetch_result() helper to t/t5526-fetch-submodules.sh that asserts on the output of "git fetch --recurse-submodules" and handles the ordering of expect.err. As a result, the tests no longer construct expect.err manually. Tests still consider the old head of the remote-tracking branch ("$head1"), but that will be fixed in a later commit. Signed-off-by: Glen Choo <chooglen@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>