ww test: report no tests to run

lib/test/run.ww

@@ -116,8 +116,7 @@ export fn run(tests: [](str, *fn() void)) i32 = {
 		return 0;
 	};
 	if (selected == 0) {
-		if (pkgprefix.len != 0) { tstputs("[no matches]\n"); }
-		else { tstputs("No tests run\n"); };
+		tsterrputs("testing: warning: no tests to run\n");
 		tstputaccounting(tests.len, 0, 0, 0);
 		return 0;
 	};
@@ -626,6 +625,10 @@ fn tstputs(s: str) void = {
 	tstfdwriteall(os.STDOUT_FILENO, s.ptr, s.len: u64);
 };
 
+fn tsterrputs(s: str) void = {
+	tstfdwriteall(os.STDERR_FILENO, s.ptr, s.len: u64);
+};
+
 fn tstputuint(n: i32) void = {
 	let buf: [16]u8;
 	let i: i32 = 16;