t7408: merge short tests, factor out testing method

Tests consisting of one line each can be consolidated to have fewer tests
to run as well as fewer lines of code.

When having just a few git commands, do not create a new shell but
use the -C flag in Git to execute in the correct directory.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7408-submodule-reference.sh

@@ -8,6 +8,15 @@ test_description='test clone --reference'
 
 base_dir=$(pwd)
 
+test_alternate_is_used () {
+	alternates_file="$1" &&
+	working_dir="$2" &&
+	test_line_count = 1 "$alternates_file" &&
+	echo "0 objects, 0 kilobytes" >expect &&
+	git -C "$working_dir" count-objects >actual &&
+	test_cmp expect actual
+}
+
 test_expect_success 'preparing first repository' '
 	test_create_repo A &&
 	(
@@ -40,16 +49,14 @@ test_expect_success 'preparing superproject' '
 	)
 '
 
-test_expect_success 'submodule add --reference' '
+test_expect_success 'submodule add --reference uses alternates' '
 	(
 		cd super &&
 		git submodule add --reference ../B "file://$base_dir/A" sub &&
-		git commit -m B-super-added
-	)
-'
-
-test_expect_success 'after add: existence of info/alternates' '
-	test_line_count = 1 super/.git/modules/sub/objects/info/alternates
+		git commit -m B-super-added &&
+		git repack -ad
+	) &&
+	test_alternate_is_used super/.git/modules/sub/objects/info/alternates super/sub
 '
 
 test_expect_success 'that reference gets used with add' '
@@ -61,23 +68,18 @@ test_expect_success 'that reference gets used with add' '
 	)
 '
 
-test_expect_success 'cloning superproject' '
-	git clone super super-clone
-'
-
-test_expect_success 'update with reference' '
-	cd super-clone && git submodule update --init --reference ../B
-'
-
-test_expect_success 'after update: existence of info/alternates' '
-	test_line_count = 1 super-clone/.git/modules/sub/objects/info/alternates
-'
+# The tests up to this point, and repositories created by them
+# (A, B, super and super/sub), are about setting up the stage
+# for subsequent tests and meant to be kept throughout the
+# remainder of the test.
+# Tests from here on, if they create their own test repository,
+# are expected to clean after themselves.
 
-test_expect_success 'that reference gets used with update' '
-	cd super-clone/sub &&
-	echo "0 objects, 0 kilobytes" >expected &&
-	git count-objects >current &&
-	diff expected current
+test_expect_success 'updating superproject keeps alternates' '
+	test_when_finished "rm -rf super-clone" &&
+	git clone super super-clone &&
+	git -C super-clone submodule update --init --reference ../B &&
+	test_alternate_is_used super-clone/.git/modules/sub/objects/info/alternates super-clone/sub
 '
 
 test_done