add test from PR#9799

testsuite/tests/typing-gadts/pr9799.ml

@@ -0,0 +1,23 @@
+(* TEST
+   * expect
+*)
+
+type 'a t =
+  | A: [`a|`z] t
+  | B: [`b|`z] t
+;;
+[%%expect{|
+type 'a t = A : [ `a | `z ] t | B : [ `b | `z ] t
+|}];;
+
+let fn: type a. a t -> a -> int = fun x y ->
+  match (x, y) with
+  | (A, `a)
+  | (B, `b) -> 0
+  | (A, `z)
+  | (B, `z) -> 1
+;;
+[%%expect{|
+Uncaught exception: File "typing/patterns.ml", line 199, characters 21-27: Assertion failed
+
+|}];;