test-lib: Add support for multiple test prerequisites

Change the test_have_prereq function in test-lib.sh to support a
comma-separated list of prerequisites. This is useful for tests that
need e.g. both POSIXPERM and SANITY.

The implementation was stolen from Junio C Hamano and Johannes Sixt,
the tests and documentation were not. See the "Tests in Cygwin" thread
in May 2009 for the originals:

    http://thread.gmane.org/gmane.comp.version-control.git/116729/focus=118385
    http://thread.gmane.org/gmane.comp.version-control.git/116729/focus=118434

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

t/README

@@ -350,6 +350,12 @@ library for your script to use.
 	test_expect_success TTY 'git --paginate rev-list uses a pager' \
 	    ' ... '
 
+   You can also supply a comma-separated list of prerequisites, in the
+   rare case where your test depends on more than one:
+
+	test_expect_success PERL,PYTHON 'yo dawg' \
+	    ' test $(perl -E 'print eval "1 +" . qx[python -c "print 2"]') == "4" '
+
  - test_expect_failure [<prereq>] <message> <script>
 
    This is NOT the opposite of test_expect_success, but is used

t/t0000-basic.sh

@@ -73,6 +73,23 @@ then
 	exit 1
 fi
 
+test_set_prereq HAVETHIS
+haveit=no
+test_expect_success HAVETHIS,HAVEIT 'test runs if prerequisites are satisfied' '
+    test_have_prereq HAVEIT &&
+    test_have_prereq HAVETHIS &&
+    haveit=yes
+'
+donthaveit=yes
+test_expect_success HAVEIT,DONTHAVEIT 'unmet prerequisites causes test to be skipped' '
+    donthaveit=no
+'
+if test $haveit$donthaveit != yesyes
+then
+	say "bug in test framework: multiple prerequisite tags do not work reliably"
+	exit 1
+fi
+
 clean=no
 test_expect_success 'tests clean up after themselves' '
     test_when_finished clean=yes

t/test-lib.sh

@@ -327,12 +327,20 @@ test_set_prereq () {
 satisfied=" "
 
 test_have_prereq () {
+	# prerequisites can be concatenated with ','
+	save_IFS=$IFS
+	IFS=,
+	set -- $*
+	IFS=$save_IFS
+	for prerequisite
+	do
 		case $satisfied in
-	*" $1 "*)
+		*" $prerequisite "*)
 			: yes, have it ;;
 		*)
 			! : nope ;;
 		esac
+	done
 }
 
 # You are not expected to call test_ok_ and test_failure_ directly, use