tests: list available tests if an invalid test name is given
diff --git a/tests/weston-test-runner.c b/tests/weston-test-runner.c
index fefb93b..ed5baf0 100644
--- a/tests/weston-test-runner.c
+++ b/tests/weston-test-runner.c
@@ -82,6 +82,7 @@
 		t = find_test(argv[1]);
 		if (t == NULL) {
 			fprintf(stderr, "unknown test: \"%s\"\n", argv[1]);
+			list_tests();
 			exit(EXIT_FAILURE);
 		}