t5561: skip tests if curl is not available

It's possible to have libcurl installed but not the curl
command-line utility. The latter is not generally needed for
Git's http support, but we use it in t5561 for basic tests
of http-backend's functionality. Let's detect when it's
missing and skip this test.

Note that we can't mark the individual tests with the CURL
prerequisite. They're in a shared t556x_common that uses the
GET and POST functions as a level of indirection, and it's
only our implementations of those functions in t5561 that
requires curl. It's not a problem, though, as literally
every test in the script would depend on the prerequisite
anyway.

Reported-by: Jens Krüger <[email protected]>
Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

t/t5561-http-backend.sh

@@ -3,6 +3,12 @@
 test_description='test git-http-backend'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-httpd.sh
+
+if ! test_have_prereq CURL; then
+	skip_all='skipping raw http-backend tests, curl not available'
+	test_done
+fi
+
 start_httpd
 
 GET() {

t/test-lib.sh

@@ -1187,3 +1187,7 @@ test_lazy_prereq LONG_IS_64BIT '
 
 test_lazy_prereq TIME_IS_64BIT 'test-date is64bit'
 test_lazy_prereq TIME_T_IS_64BIT 'test-date time_t-is64bit'
+
+test_lazy_prereq CURL '
+	curl --version
+'