reflog test: test interaction with detached HEAD

A proposed patch produced broken HEAD reflog entries when checking out
anything other than a branch.  The testsuite still passed, so it took
a few days for the bug to be noticed.

Add tests checking the content of the reflog after detaching and
reattaching HEAD so we don't have to rely on manual testing to catch
such problems in the future.

[jn: using 'log -g --format=%H' instead of parsing --oneline output,
 resetting state in each test so they can be safely reordered or
 skipped]

Signed-off-by: Jonathan Nieder <[email protected]>
Reviewed-by: Ronnie Sahlberg <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

t/t1413-reflog-detach.sh

@@ -0,0 +1,70 @@
+#!/bin/sh
+
+test_description='Test reflog interaction with detached HEAD'
+. ./test-lib.sh
+
+reset_state () {
+	git checkout master &&
+	cp saved_reflog .git/logs/HEAD
+}
+
+test_expect_success setup '
+	test_tick &&
+	git commit --allow-empty -m initial &&
+	git branch side &&
+	test_tick &&
+	git commit --allow-empty -m second &&
+	cat .git/logs/HEAD >saved_reflog
+'
+
+test_expect_success baseline '
+	reset_state &&
+	git rev-parse master master^ >expect &&
+	git log -g --format=%H >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'switch to branch' '
+	reset_state &&
+	git rev-parse side master master^ >expect &&
+	git checkout side &&
+	git log -g --format=%H >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'detach to other' '
+	reset_state &&
+	git rev-parse master side master master^ >expect &&
+	git checkout side &&
+	git checkout master^0 &&
+	git log -g --format=%H >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'detach to self' '
+	reset_state &&
+	git rev-parse master master master^ >expect &&
+	git checkout master^0 &&
+	git log -g --format=%H >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'attach to self' '
+	reset_state &&
+	git rev-parse master master master master^ >expect &&
+	git checkout master^0 &&
+	git checkout master &&
+	git log -g --format=%H >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'attach to other' '
+	reset_state &&
+	git rev-parse side master master master^ >expect &&
+	git checkout master^0 &&
+	git checkout side &&
+	git log -g --format=%H >actual &&
+	test_cmp expect actual
+'
+
+test_done