t3301: fix false negative

In 6956f85 (notes: implement helpers needed for note copying during
rewrite, 2010-03-12), we introduced a test case that verifies that the
config setting `notes.rewriteRef` can be overridden via the environment
variable `GIT_NOTES_REWRITE_REF`.

Back when it was introduced, it relied on a side effect of an earlier
test case that configured `core.noteRef` to point to `refs/notes/other`.

In 908a320 (t3301: modernize style, 2014-11-12), this side effect was
removed.

The test case *still* passed, but for the wrong reason: we no longer
overrode the rewrite ref, but there simply was nothing to rewrite
anymore, as the overridden notes ref was "modernized" away.

Let's let that test case pass for the correct reason again.

To make sure of that, let's change the idea of the original test case:
it configured `notes.rewriteRef` to point to the actual notes ref,
forced that to be ignored and then verified that the notes were *not*
rewritten.

By turning that idea upside down (configure the `notes.rewriteRef` to
another notes ref, override it via the environment variable to force the
notes to be copied, and then verify that the notes *were* rewritten), we
make it much harder for that test case to pass for the wrong reason.

Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dscho

t/t3301-notes.sh

@@ -1120,9 +1120,10 @@ test_expect_success 'GIT_NOTES_REWRITE_REF overrides config' '
 	test_config notes.rewriteMode overwrite &&
 	test_config notes.rewriteRef refs/notes/other &&
 	echo $(git rev-parse HEAD^) $(git rev-parse HEAD) |
-	GIT_NOTES_REWRITE_REF= git notes copy --for-rewrite=foo &&
+	GIT_NOTES_REWRITE_REF=refs/notes/commits \
+		git notes copy --for-rewrite=foo &&
 	git log -1 >actual &&
-	test_cmp expect actual
+	grep "replacement note 3" actual
 '
 
 test_expect_success 'git notes copy diagnoses too many or too few parameters' '