t6004: add a bit more path optimization test.

Signed-off-by: NJunio C Hamano <junkio@cox.net>

t/t6004-rev-list-path-optim.sh

@@ -7,7 +7,8 @@ test_description='git-rev-list trivial path optimization test'
 test_expect_success setup '
 echo Hello > a &&
 git add a &&
-git commit -m "Initial commit" a
+git commit -m "Initial commit" a &&
+initial=$(git rev-parse --verify HEAD)
 '
 
 test_expect_success path-optimization '
@@ -16,4 +17,35 @@ test_expect_success path-optimization '
     test $(git-rev-list $commit -- . | wc -l) = 1
 '
 
+test_expect_success 'further setup' '
+	git checkout -b side &&
+	echo Irrelevant >c &&
+	git add c &&
+	git commit -m "Side makes an irrelevant commit" &&
+	echo "More Irrelevancy" >c &&
+	git add c &&
+	git commit -m "Side makes another irrelevant commit" &&
+	echo Bye >a &&
+	git add a &&
+	git commit -m "Side touches a" &&
+	side=$(git rev-parse --verify HEAD) &&
+	echo "Yet more Irrelevancy" >c &&
+	git add c &&
+	git commit -m "Side makes yet another irrelevant commit" &&
+	git checkout master &&
+	echo Another >b &&
+	git add b &&
+	git commit -m "Master touches b" &&
+	git merge side &&
+	echo Touched >b &&
+	git add b &&
+	git commit -m "Master touches b again"
+'
+
+test_expect_success 'path optimization 2' '
+	( echo "$side"; echo "$initial" ) >expected &&
+	git rev-list HEAD -- a >actual &&
+	diff -u expected actual
+'
+
 test_done