diff --git a/builtin/my_show_test.mbt b/builtin/my_show_test.mbt
new file mode 100644
index 000000000..60a28300a
--- /dev/null
+++ b/builtin/my_show_test.mbt
@@ -0,0 +1,45 @@
+
+trait MyShow {
+  my_output(Self, Logger) -> Unit
+  my_to_string(Self) -> String
+}
+impl MyShow with my_output(self, logger) {
+  logger.write_string(MyShow::my_to_string(self))
+}
+
+impl MyShow with my_to_string(self) {
+  let logger = StringBuilder::new()
+  self.my_output(logger)
+  logger.to_string()
+}
+
+type X  Int
+
+// fn my_to_string(self: X) -> String {
+//   self._.to_string()
+// }
+
+
+test {
+  let u = X(42)  
+  inspect!(u.my_to_string()) // this fails type checker
+  let u0 = u as MyShow // this works, it should fail
+  inspect!(u0.my_to_string())
+  ignore(u0)  
+}
+
+type Y Int 
+
+fn my_to_string(self: Y) -> String {
+  self._.to_string()
+}
+
+impl MyShow for Y with my_to_string(self) {
+  self.my_to_string()
+}
+test {
+  let sb = StringBuilder::new()
+  let v = Y(42)
+  v.my_output(sb)
+  inspect!(sb.to_string(), content="42")
+}
\ No newline at end of file