Re: [PATCH v2 01/12] t5520: implement tests for no merge candidates cases

Commit a8c9bef4 fully established the current advices given by git-pull
for the different cases where git-fetch will not have anything marked
for merge:

1. We fetched from a specific remote, and a refspec was given, but it
    ended up not fetching anything. This is usually because the user
    provided a wildcard refspec which had no matches on the remote end.

2. We fetched from a non-default remote, but didn't specify a branch to
    merge. We can't use the configured one because it applies to the
    default remote, and thus the user must specify the branches to merge.

3. We fetched from the branch's or repo's default remote, but:

    a. We are not on a branch, so there will never be a configured branch
       to merge with.

    b. We are on a branch, but there is no configured branch to merge
       with.

4. We fetched from the branch's or repo's default remote, but the
    configured branch to merge didn't get fetched (either it doesn't
    exist, or wasn't part of the configured fetch refspec)

Implement tests for the above 5 cases to ensure that the correct code
paths are triggered for each of these cases.

Signed-off-by: Paul Tan <redacted>
---

Notes:
     * Re-worded commit message to match the logic used in git-pull.sh's
       error_on_no_merge_candidates().
     
     * The tests have thus also been reordered to match the commit message.
     
     * Non-hackish solution for case 3a.
     
     * Add more checks to ensure that git-pull does not touch any files it
       should not be touching on failure.

  t/t5520-pull.sh | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 55 insertions(+)

diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
index 7efd45b..5add900 100755
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh

@@ -109,6 +109,61 @@ test_expect_success 'the default remote . should not break explicit pull' '
  	test `cat file` = modified
  '
  
+test_expect_success 'fail if wildcard spec does not match any refs' '
+	git checkout -b test copy^ &&
+	test_when_finished "git checkout -f copy && git branch -D test" &&
+	test `cat file` = file &&