Hi Junio, On 17 Mar 2022, at 17:10, Junio C Hamano wrote: > "John Cai via GitGitGadget" <gitgitgadget@xxxxxxxxx> writes: > >> From: John Cai <johncai86@xxxxxxxxx> >> >> Currently when rebase is used with a non branch, and <oid> is up to >> date with base: >> >> git rebase base <oid> >> >> It will update the ref that HEAD is pointing at to <oid>, and leave HEAD >> unmodified. >> >> This is a bug. The expected behavior is that the branch HEAD points at >> remains unmodified while HEAD is updated to point to <oid> in detached >> HEAD mode. > > Never do tests this way. > > The primary reason why we do not want to write our tests the way > this patch does is because we do not _care_ how it is broken in the > behaviour of the original code. 'main' moving out of $old_main is > the bug we care about. It is still buggy if it did not move to > Second, but some other commit. Yet this patch insists that 'main' > to move to Second and nothing else. What we want is 'main' to stay > at $old_main in the end anyway, and we should directly test that > condition. I was attemping to follow the advice to "show" vs "tell" in [1]. All this make sense to me however. > > If you insist to have two commits (which I strongly recommend > against in this case), you write a test that makes sure that 'main' > stays at $old_main, but mark the test with test_expect_failure. And > then later in the step that fixes the code, flip "expect_failure" to > "expect_success". > > But it is not ideal, either. Imagine what you see in "git show" > output of the commit that fixed the problem. Most of the test that > shows the behaviour that the commit _cares_ about will be outside > post-context of the hunk that flips test_expect_failure to > test_expect_success. > > The best and the simplest way, for a simple case like this, to write > test is to add the test to expect what we want to see in the end, > and do so in the same commit as the one that corrects the behaviour > of the code. If somebody wants to see what the breakage looks like, > it is easy to > > (1) checkout the commit that fixes the code and adds such a test, > > (2) tentatively revert everything outside t/, and > > (3) run the test with "-i -v" options. > > Then test_expect_success that wants to see 'main' to stay at > $old_main will show that 'main' moved by a test failure. Working > from a patch is the same way, i.e. you can apply only the parts > inside t/ and run the current code to see the breakage, and then > apply the rest to see the fix. > >> +test_expect_success 'switch to non-branch changes branch HEAD points to' ' >> + git checkout main && >> + old_main=$(git rev-parse HEAD) && >> + git rebase First Second^0 && > >> + test_cmp_rev HEAD main && >> + test_cmp_rev main $(git rev-parse Second) && >> + git symbolic-ref HEAD > > I already said that the second one should expect main to be at > $old_main, but the "HEAD and main are the same" and "HEAD is a > symolic-ref" test can be replaced with a single test that is "HEAD > is a symbolic-ref to 'main'", which would be more strict. I.e. > > test "$(git symbolic-ref HEAD)" = refs/heads/main && > test_cmp_rev main "$old_main" > > And such a test that expects the correct behaviour we want to have > in the end should be added in [PATCH 3/3] when the code is fixed, > not here in a separate commit. 1. https://lore.kernel.org/git/220317.86r170d6zs.gmgdl@xxxxxxxxxxxxxxxxxxx/ > >> +' > > Thanks.
