Add sv_stream_insert_test

include/boost/core/string_view.hpp

@@ -928,7 +928,38 @@ public:
 
 template<class Ch> std::basic_ostream<Ch>& operator<<( std::basic_ostream<Ch>& os, basic_string_view<Ch> str )
 {
-    os.write( str.data(), str.size() );
+    Ch const* p = str.data();
+    std::size_t n = str.size();
+
+    if( n == 0 )
+    {
+        os << "";
+    }
+    else
+    {
+        std::size_t m = os.width();
+
+        if( n >= m )
+        {
+            os.write( p, n );
+        }
+        else if( ( os.flags() & std::ios_base::adjustfield ) == std::ios_base::left )
+        {
+            os.write( p, n - 1 );
+
+            os.width( m - n + 1 );
+            os << p[ n-1 ];
+        }
+        else
+        {
+            os.width( m - n + 1 );
+            os << p[0];
+
+            os.write( p + 1, n - 1 );
+        }
+    }
+
+    os.width( 0 );
     return os;
 }