Add test for show polymorphic variant @printer

Author: sim642

src_test/show/test_deriving_show.cppo.ml

@@ -233,6 +233,25 @@ let test_variant_printer ctxt =
   assert_equal ~printer
     "fourth: 8 4" (show_variant_printer (Fourth(8,4)))
 
+type poly_variant_printer = [
+  | `First [@printer fun fmt _ -> Format.pp_print_string fmt "first"]
+  | `Second of int [@printer fun fmt i -> fprintf fmt "second: %d" i]
+  | `Third
+  | `Fourth of int * int
+                [@printer fun fmt (a,b) -> fprintf fmt "fourth: %d %d" a b]
+]
+[@@deriving show]
+
+let test_poly_variant_printer ctxt =
+  assert_equal ~printer
+    "first" (show_poly_variant_printer `First);
+  assert_equal ~printer
+    "second: 42" (show_poly_variant_printer (`Second 42));
+  assert_equal ~printer
+    "`Third" (show_poly_variant_printer `Third);
+  assert_equal ~printer
+    "fourth: 8 4" (show_poly_variant_printer (`Fourth(8,4)))
+
 type no_full    = NoFull   of int [@@deriving show { with_path = false }]
 type with_full  = WithFull of int [@@deriving show { with_path = true  }]
 module WithFull = struct
@@ -264,6 +283,7 @@ let suite = "Test deriving(show)" >::: [
     "test_std_shadowing"   >:: test_std_shadowing;
     "test_poly_app"        >:: test_poly_app;
     "test_variant_printer" >:: test_variant_printer;
+    "test_poly_variant_printer" >:: test_poly_variant_printer;
     "test_paths"           >:: test_paths_printer;
     "test_result"          >:: test_result;
     "test_result_result"   >:: test_result_result;