wcc: reject exported/bodyless/duplicate @test shapes

Both frontends, byte-stable fragments; -T-mode checks, so the rows
live in test/package (the fixture compile cell cannot reach -T).

cmd/wcc/check.c

@@ -3230,14 +3230,31 @@ check_file(Checker *c, Node *file)
 		for (Node *d = file->list; d; d = d->next) {
 			if (d->kind != N_FNDECL)
 				continue;
-			int istest = 0;
+			int ntestattr = 0;
 			for (Node *at = d->attr; at; at = at->next)
-				if (at->str && strcmp(at->str, "test") == 0) {
-					istest = 1;
-					break;
-				}
-			if (!istest)
+				if (at->str && strcmp(at->str, "test") == 0)
+					ntestattr++;
+			if (ntestattr == 0)
 				continue;
+			/* Attribute-shape rejects, fixed order, first failure
+			 * wins per fn; wording is byte-stable with the wwstage
+			 * twin (check.ww). A silently-dropped shape here ships
+			 * a test that never runs. */
+			if (ntestattr > 1) {
+				err(c, d->pos, "duplicate @test on fn '%s'",
+				    d->str);
+				continue;
+			}
+			if (d->export) {
+				err(c, d->pos, "@test fn '%s' cannot be exported",
+				    d->str);
+				continue;
+			}
+			if (d->body == NULL) {
+				err(c, d->pos, "@test fn '%s' needs a body",
+				    d->str);
+				continue;
+			}
 			/* `fn f() void` parses the explicit `void` into d->lhs
 			 * (parse.c:1329), so void-returning is lhs==NULL OR an
 			 * N_TNAME "void" — not lhs==NULL alone. */