fix test when input is output range, which should fail

Author: changkhothuychung

libcxx/test/std/ranges/range.adaptors/range.concat/ctor.default.pass.cpp

@@ -69,13 +69,6 @@ constexpr bool test() {
     }
   }
 
-  // check when input is an output range, which should be well-formed
-  {
-    std::vector<int> v{1, 2, 3};
-    auto r = std::views::counted(std::back_inserter(v), 3);
-    static_assert(!std::ranges::input_range<decltype(r)>);
-  }
-
   return true;
 }
 

libcxx/test/std/ranges/range.adaptors/range.concat/ctor.default.verify.cpp

@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++26
+
+#include <cassert>
+#include <ranges>
+#include <vector>
+#include "test_macros.h"
+
+int main(int, char**) {
+  std::vector<int> v{1, 2, 3};
+  auto r = std::views::counted(std::back_inserter(v), 3);
+  auto c = std::views::concat(r);
+  // expected-error@*:* {{}}
+
+  return 0;
+}