add the missing test

test/tla/PolyTooGeneral.tla

@@ -0,0 +1,7 @@
+---------------------- MODULE PolyTooGeneral ------------------------------
+\* A library author did not think carefully about the types
+\* and wrote a too general type. The type checker should complain.
+\*
+\* @type: a => b;
+Id(x) == x
+===========================================================================