Add more tests for std::ws as pointed out by bug #19497

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@206770 91177308-0d34-0410-b5e6-96231b3b80d8

test/input.output/iostream.format/input.streams/istream.manip/ws.pass.cpp

@@ -56,4 +56,24 @@ int main()
         assert(is.good());
         assert(is.peek() == L'1');
     }
+    {
+        testbuf<char> sb("  ");
+        std::istream is(&sb);
+        ws(is);
+        assert(!is.fail());
+        assert(is.eof());
+        ws(is);
+        assert(is.eof());
+        assert(is.fail());
+    }
+    {
+        testbuf<wchar_t> sb(L"  ");
+        std::wistream is(&sb);
+        ws(is);
+        assert(!is.fail());
+        assert(is.eof());
+        ws(is);
+        assert(is.eof());
+        assert(is.fail());
+    }
 }