unikernel/duniverse/ppxlib/test/501_migrations/one_migration.t

@@ -0,0 +1,45 @@
+This test is enabled both on 5.0.0 and 5.1.0. The test makes sense for as long
+as the ppxlib AST is either 5.0.0 or 5.1.0. While the ppxlib AST is on 5.0.0, the
+test checks whether parsing on 5.0.0 (result of test running on 5.0.0) is the same as
+parsing on 5.1.0 and then migrating down to 5.0.0 (result of test running on 5.1.0).
+
+The test is mostly useful for debugging problems in a full round-trip.
+
+  $ echo "let x : int = 5" > file.ml
+  $ ./identity_driver.exe -dparsetree file.ml
+  [ Pstr_value
+      ( Nonrecursive
+      , [ { pvb_pat = Ppat_var "x"
+          ; pvb_expr = Pexp_constant (Pconst_integer ( "5", None))
+          ; pvb_constraint =
+              Some
+                (Pvc_constraint
+                   { locally_abstract_univars = []
+                   ; typ = Ptyp_constr ( Lident "int", [])
+                   })
+          ; pvb_attributes = __attrs
+          ; pvb_loc = __loc
+          }
+        ]
+      )
+  ]
+
+  $ cat > file.ml << EOF
+  > module F () = struct end
+  > module M = F ()
+  > EOF
+
+  $ ./identity_driver.exe -dparsetree file.ml
+  [ Pstr_module
+      { pmb_name = Some "F"
+      ; pmb_expr = Pmod_functor ( Unit, Pmod_structure [])
+      ; pmb_attributes = __attrs
+      ; pmb_loc = __loc
+      }
+  ; Pstr_module
+      { pmb_name = Some "M"
+      ; pmb_expr = Pmod_apply_unit (Pmod_ident (Lident "F"))
+      ; pmb_attributes = __attrs
+      ; pmb_loc = __loc
+      }
+  ]