test_must_fail do_checkout branch2 $HEAD2
'
+test_expect_success 'checkout -B to an existing branch resets branch to HEAD' '
+ git checkout branch1 &&
+
+ do_checkout branch2 "" -B
+'
+
+test_expect_success 'checkout -B to an existing branch from detached HEAD resets branch to HEAD' '
+ git checkout $(git rev-parse --verify HEAD) &&
+
+ do_checkout branch2 "" -B
+'
+
+test_expect_success 'checkout -B to an existing branch with an explicit ref resets branch to that ref' '
+ git checkout branch1 &&
+
+ do_checkout branch2 $HEAD1 -B
+'
+
+test_expect_success 'checkout -B to an existing branch with unmergeable changes fails' '
+ git checkout branch1 &&
+
+ setup_dirty_unmergeable &&
+ test_must_fail do_checkout branch2 $HEAD1 -B &&
+ test_dirty_unmergeable
+'
+
+test_expect_success 'checkout -f -B to an existing branch with unmergeable changes discards changes' '
+ # still dirty and on branch1
+ do_checkout branch2 $HEAD1 "-f -B" &&
+ test_must_fail test_dirty_unmergeable
+'
+
+test_expect_success 'checkout -B to an existing branch preserves mergeable changes' '
+ git checkout branch1 &&
+
+ setup_dirty_mergeable &&
+ do_checkout branch2 $HEAD1 -B &&
+ test_dirty_mergeable
+'
+
+test_expect_success 'checkout -f -B to an existing branch with mergeable changes discards changes' '
+ # clean up from previous test
+ git reset --hard &&
+
+ git checkout branch1 &&
+
+ setup_dirty_mergeable &&
+ do_checkout branch2 $HEAD1 "-f -B" &&
+ test_must_fail test_dirty_mergeable
+'
+
test_done