Move old test into test/libcxx, and implement new version of test for ostreambuf_iterator::failed. Fixes PR#37245. Thanks to Billy O'Neill for the bug report.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@330955 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/iterators/failed.pass.cpp

@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <iterator>
+
+// class ostreambuf_iterator
+
+// bool failed() const throw();
+//
+//	Extension: constructing from NULL is UB; we just make it a failed iterator
+
+#include <iterator>
+#include <sstream>
+#include <cassert>
+
+int main()
+{
+    {
+        std::ostreambuf_iterator<char> i(nullptr);
+        assert(i.failed());
+    }
+    {
+        std::ostreambuf_iterator<wchar_t> i(nullptr);
+        assert(i.failed());
+    }
+}