vlib/v/checker/tests/mut_receiver_wrong_return_type.vv:4:9: error: cannot use `Test` as type `?int` in return argument
    2 |
    3 | fn (mut test Test) test() ?int {
    4 |     return test
      |            ~~~~
    5 | }
    6 |
vlib/v/checker/tests/mut_receiver_wrong_return_type.vv:8:9: error: cannot use `Test` as type `int` in return argument
    6 |
    7 | fn (mut test Test) test2() int {
    8 |     return test
      |            ~~~~
    9 | }