add simple tests of consistency across rebase types

Helped-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Martin von Zweigbergk <martinvonz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-rebase.sh

@@ -65,3 +65,19 @@ EOF
 	test_set_editor "$(pwd)/fake-editor.sh"
 	chmod a+x fake-editor.sh
 }
+
+# checks that the revisions in "$2" represent a linear range with the
+# subjects in "$1"
+test_linear_range () {
+	revlist_merges=$(git rev-list --merges "$2") &&
+	test -z "$revlist_merges" &&
+	expected=$1
+	set -- $(git log --reverse --format=%s "$2")
+	test "$expected" = "$*"
+}
+
+reset_rebase () {
+	test_might_fail git rebase --abort &&
+	git reset --hard &&
+	git clean -f
+}

t/t3421-rebase-topology-linear.sh

@@ -0,0 +1,78 @@
+#!/bin/sh
+
+test_description='basic rebase topology tests'
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-rebase.sh
+
+# a---b---c
+#      \
+#       d---e
+test_expect_success 'setup' '
+	test_commit a &&
+	test_commit b &&
+	test_commit c &&
+	git checkout b &&
+	test_commit d &&
+	test_commit e
+'
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "simple rebase $*" "
+		reset_rebase &&
+		git rebase $* c e &&
+		test_cmp_rev c HEAD~2 &&
+		test_linear_range 'd e' c..
+	"
+}
+test_run_rebase success ''
+test_run_rebase success -m
+test_run_rebase success -i
+test_run_rebase success -p
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* is no-op if upstream is an ancestor" "
+		reset_rebase &&
+		git rebase $* b e &&
+		test_cmp_rev e HEAD
+	"
+}
+test_run_rebase success ''
+test_run_rebase success -m
+test_run_rebase success -i
+test_run_rebase success -p
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* -f rewrites even if upstream is an ancestor" "
+		reset_rebase &&
+		git rebase $* -f b e &&
+		! test_cmp_rev e HEAD &&
+		test_cmp_rev b HEAD~2 &&
+		test_linear_range 'd e' b..
+	"
+}
+test_run_rebase success ''
+test_run_rebase success -m
+test_run_rebase success -i
+test_run_rebase failure -p
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* fast-forwards from ancestor of upstream" "
+		reset_rebase &&
+		git rebase $* e b &&
+		test_cmp_rev e HEAD
+	"
+}
+test_run_rebase success ''
+test_run_rebase success -m
+test_run_rebase success -i
+test_run_rebase success -p
+
+test_done