Insist that tests start out with the magic string "varnishtest[:whitespace:]"

bin/varnishtest/vtc_main.c

@@ -34,6 +34,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 
+#include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <poll.h>
@@ -529,6 +530,13 @@ main(int argc, char * const *argv)
 				continue;
 			exit(2);
 		}
+		if (strncmp(p, "varnishtest", 11) || !isspace(p[11])) {
+			fprintf(stderr, "File \"%s\" doesn't start with 'varnishtest'\n",
+			    *argv);
+			if (vtc_continue)
+				continue;
+			exit(2);
+		}
 		ALLOC_OBJ(tp, TST_MAGIC);
 		AN(tp);
 		tp->filename = *argv;