diff --git a/map_container.m b/map_container.m
index eac8543..cdfaa78 100644
--- a/map_container.m
+++ b/map_container.m
@@ -42,4 +42,8 @@ assert(isequal( values(pairs), {"Hello", "Enrico"} ));
 assert(isequal( pairs('Msg'), "Hello" ));
 
 % change a value
-pairs('Msg') = "World";
\ No newline at end of file
+pairs('Msg') = "World";
+
+% check for key existence
+assert(isequal(pairs.isKey('Msg'), true));
+assert(isequal(pairs.isKey('Test'), false));