test: git-stash conflict sets up rerere

Add a test to make sure that a conflicted "stash apply" invokes
rerere to record the conflicts and resolve the the files it can
(the current code doesn't, so the test is marked as failing).

Without correct state recorded for rerere, mergetool may be
confused, causing it to think no files have conflicts even though
they do.  This condition is not verified by this test since a
subsequent commit will change the behavior to enable rerere for
stash conflicts.

Also, the next test expected us to finish up with a reset, which is
impossible to do if we fail (as we must) and it's an unreasonable
expectation anyway.  Begin the next test with a reset of its own
instead.

Signed-off-by: Phil Hord <hordp@cisco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7610-mergetool.sh

@@ -55,6 +55,16 @@ test_expect_success 'setup' '
     git rm file12 &&
     git commit -m "branch1 changes" &&
 
+    git checkout -b stash1 master &&
+    echo stash1 change file11 >file11 &&
+    git add file11 &&
+    git commit -m "stash1 changes" &&
+
+    git checkout -b stash2 master &&
+    echo stash2 change file11 >file11 &&
+    git add file11 &&
+    git commit -m "stash2 changes" &&
+
     git checkout master &&
     git submodule update -N &&
     echo master updated >file1 &&
@@ -193,7 +203,35 @@ test_expect_success 'mergetool skips resolved paths when rerere is active' '
     git reset --hard
 '
 
+test_expect_failure 'conflicted stash sets up rerere'  '
+    git config rerere.enabled true &&
+    git checkout stash1 &&
+    echo "Conflicting stash content" >file11 &&
+    git stash &&
+
+    git checkout --detach stash2 &&
+    test_must_fail git stash apply &&
+
+    test -n "$(git ls-files -u)" &&
+    conflicts="$(git rerere remaining)" &&
+    test "$conflicts" = "file11" &&
+    output="$(git mergetool --no-prompt)" &&
+    test "$output" != "No files need merging" &&
+
+    git commit -am "save the stash resolution" &&
+
+    git reset --hard stash2 &&
+    test_must_fail git stash apply &&
+
+    test -n "$(git ls-files -u)" &&
+    conflicts="$(git rerere remaining)" &&
+    test -z "$conflicts" &&
+    output="$(git mergetool --no-prompt)" &&
+    test "$output" = "No files need merging"
+'
+
 test_expect_success 'mergetool takes partial path' '
+    git reset --hard
     git config rerere.enabled false &&
     git checkout -b test12 branch1 &&
     git submodule update -N &&