Improve t6029 to check the real "subtree" case

t6029 already checks if subtree available and works like recursive. This
patch adds code to test test the extra functionality the subtree merge
strategy provides.
Signed-off-by: NMiklos Vajna <vmiklos@frugalware.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t6029-merge-subtree.sh

@@ -29,4 +29,51 @@ test_expect_success 'subtree available and works like recursive' '
 
 '
 
+test_expect_success 'setup' '
+	mkdir git-gui &&
+	cd git-gui &&
+	git init &&
+	echo git-gui > git-gui.sh &&
+	o1=$(git hash-object git-gui.sh) &&
+	git add git-gui.sh &&
+	git commit -m "initial git-gui" &&
+	cd .. &&
+	mkdir git &&
+	cd git &&
+	git init &&
+	echo git >git.c &&
+	o2=$(git hash-object git.c) &&
+	git add git.c &&
+	git commit -m "initial git"
+'
+
+test_expect_success 'initial merge' '
+	git remote add -f gui ../git-gui &&
+	git merge -s ours --no-commit gui/master &&
+	git read-tree --prefix=git-gui/ -u gui/master &&
+	git commit -m "Merge git-gui as our subdirectory" &&
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o1 0	git-gui/git-gui.sh"
+		echo "100644 $o2 0	git.c"
+	) >expected &&
+	git diff -u expected actual
+'
+
+test_expect_success 'merge update' '
+	cd ../git-gui &&
+	echo git-gui2 > git-gui.sh &&
+	o3=$(git hash-object git-gui.sh) &&
+	git add git-gui.sh &&
+	git commit -m "update git-gui" &&
+	cd ../git &&
+	git pull -s subtree gui master &&
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o3 0	git-gui/git-gui.sh"
+		echo "100644 $o2 0	git.c"
+	) >expected &&
+	git diff -u expected actual
+'
+
 test_done