[TESTS][LAMBDA] Add test identity_precise in union

tests/lambda/src/main.ml

@@ -161,6 +161,11 @@ let tests_eval = "CDuce runtime tests (Typed -> Lambda -> Value)" >:::
     );
 
     "union" >:: ( fun test_ctxt ->
+      assert_equal ~msg:"Test CDuce.runtime.union.identity_precise failed"
+      ~printer:(fun x -> x) "Abstraction((Int -> Int & X1 -> X1 where X1 = [ Char* ], Int -> Int &
+                                                         X1 -> X1 where
+                                                         X1 = [ Char* ]),{})"
+	(run_test_eval "fun _f f : ((Int -> Int) & (String -> String)) : ((Int -> Int) & (String -> String)) -> f");
       assert_equal ~msg:"Test CDuce.runtime.union.identity failed"
       ~printer:(fun x -> x) "Abstraction(([ Char* ] | Int, [ Char* ] | Int),{})"
 	(run_test_eval "fun f x : (Int | String) : (Int | String) -> x");