t/t3437: use named commits in the tests

Use the named commits in the tests so that they will still refer to the
same commit if the setup gets changed in the future whereas 'branch~2'
will change which commit it points to.

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Mentored-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Charvi Mendiratta <charvi077@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: charvi-077

t/t3437-rebase-fixup-options.sh

@@ -70,6 +70,7 @@ test_expect_success 'setup' '
 	echo B1 >B &&
 	test_tick &&
 	git commit --fixup=HEAD -a &&
+	git tag B1 &&
 	test_tick &&
 	git commit --allow-empty -F - <<-EOF &&
 	amend! B
@@ -91,6 +92,7 @@ test_expect_success 'setup' '
 	echo B2 >B &&
 	test_tick &&
 	FAKE_COMMIT_AMEND="edited squash" git commit --squash=HEAD -a &&
+	git tag B2 &&
 	echo B3 >B &&
 	test_tick &&
 	git commit -a -F - <<-EOF &&
@@ -104,6 +106,7 @@ test_expect_success 'setup' '
 	$EMPTY
 	edited 3
 	EOF
+	git tag B3 &&
 
 	GIT_AUTHOR_NAME="Rebase Author" &&
 	GIT_AUTHOR_EMAIL="rebase.author@example.com" &&
@@ -171,20 +174,20 @@ test_expect_success 'skipping fixup -C after fixup gives correct message' '
 '
 
 test_expect_success 'sequence of fixup, fixup -C & squash --signoff works' '
-	git checkout --detach branch &&
+	git checkout --detach B3 &&
 	FAKE_LINES="1 fixup 2 fixup_-C 3 fixup_-C 4 squash 5 fixup_-C 6" \
 		FAKE_COMMIT_AMEND=squashed \
 		FAKE_MESSAGE_COPY=actual-squash-message \
 		git -c commit.status=false rebase -ik --signoff A &&
-	git diff-tree --exit-code --patch HEAD branch -- &&
+	git diff-tree --exit-code --patch HEAD B3 -- &&
 	test_cmp_rev HEAD^ A &&
 	test_i18ncmp "$TEST_DIRECTORY/t3437/expected-squash-message" \
 		actual-squash-message
 '
 
 test_expect_success 'first fixup -C commented out in sequence fixup fixup -C fixup -C' '
 	test_when_finished "test_might_fail git rebase --abort" &&
-	git checkout branch && git checkout --detach branch~2 &&
+	git checkout --detach B2~ &&
 	git log -1 --pretty=format:%b >expected-message &&
 	FAKE_LINES="1 fixup 2 fixup_-C 3 fixup_-C 4" git rebase -i A &&
 	test_cmp_rev HEAD^ A &&
@@ -194,12 +197,11 @@ test_expect_success 'first fixup -C commented out in sequence fixup fixup -C fix
 test_expect_success 'multiple fixup -c opens editor once' '
 	test_when_finished "test_might_fail git rebase --abort" &&
 	git checkout --detach A3 &&
-	base=$(git rev-parse HEAD~4) &&
 	FAKE_COMMIT_MESSAGE="Modified-A3" \
 		FAKE_LINES="1 fixup_-C 2 fixup_-c 3 fixup_-c 4" \
 		EXPECT_HEADER_COUNT=4 \
-		git rebase -i $base &&
-	test_cmp_rev $base HEAD^ &&
+		git rebase -i A &&
+	test_cmp_rev HEAD^ A &&
 	get_author HEAD >actual-author &&
 	test_cmp expected-author actual-author &&
 	test 1 = $(git show | grep Modified-A3 | wc -l)
@@ -217,12 +219,12 @@ test_expect_success 'sequence squash, fixup & fixup -c gives combined message' '
 '
 
 test_expect_success 'fixup -C works upon --autosquash with amend!' '
-	git checkout --detach branch &&
+	git checkout --detach B3 &&
 	FAKE_COMMIT_AMEND=squashed \
 		FAKE_MESSAGE_COPY=actual-squash-message \
 		git -c commit.status=false rebase -ik --autosquash \
 						--signoff A &&
-	git diff-tree --exit-code --patch HEAD branch -- &&
+	git diff-tree --exit-code --patch HEAD B3 -- &&
 	test_cmp_rev HEAD^ A &&
 	test_i18ncmp "$TEST_DIRECTORY/t3437/expected-squash-message" \
 		actual-squash-message