tests: A SANITY test prereq for testing if we're root

Some tests depend on not being able to write to files after chmod
-w. This doesn't work when running the tests as root.

Change test-lib.sh to test if this works, and if so it sets a new
SANITY test prerequisite. The tests that use this previously failed
when run under root.

There was already a test for this in t3600-rm.sh, added by Junio C
Hamano in 2283645 in 2006. That check now uses the new SANITY
prerequisite.

Some of this was resurrected from the "Tests in Cygwin" thread in May
2009:

    http://thread.gmane.org/gmane.comp.version-control.git/116729/focus=118385

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 0 insertions, 16 deletions

diff --git a/t/t3600-rm.sh b/t/t3600-rm.sh
index b514cbb606..b26cabd571 100755
--- a/t/t3600-rm.sh
+++ b/t/t3600-rm.sh
@@ -28,22 +28,6 @@ embedded' &&
      git commit -m 'add files with tabs and newlines'
 "
 
-# Determine rm behavior
-# Later we will try removing an unremovable path to make sure
-# git rm barfs, but if the test is run as root that cannot be
-# arranged.
-: >test-file
-chmod a-w .
-rm -f test-file 2>/dev/null
-if test -f test-file
-then
-	test_set_prereq RO_DIR
-else
-	skip_all='skipping removal failure test (perhaps running as root?)'
-fi
-chmod 775 .
-rm -f test-file
-
 test_expect_success \
     'Pre-check that foo exists and is in index before git rm foo' \
     '[ -f foo ] && git ls-files --error-unmatch foo'