--- /dev/null
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='ensure rebase fast-forwards commits when possible'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+ test_commit A &&
+ test_commit B &&
+ test_commit C &&
+ test_commit D &&
+ git checkout -t -b side
+'
+
+test_rebase_same_head () {
+ status="$1" &&
+ shift &&
+ test_expect_$status "git rebase $* with $changes is no-op" "
+ oldhead=\$(git rev-parse HEAD) &&
+ test_when_finished 'git reset --hard \$oldhead' &&
+ git rebase $* &&
+ newhead=\$(git rev-parse HEAD) &&
+ test_cmp_rev \$oldhead \$newhead
+ "
+}
+
+changes='no changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to side' '
+ test_commit E
+'
+
+changes='our changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to upstream' '
+ git checkout master &&
+ test_commit F &&
+ git checkout side
+'
+
+changes='our and their changes'
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head failure --onto master... master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head failure --fork-point --onto master... master
+
+test_done