error: Error type can not change between runtime apis
  --> $DIR/mock_only_one_error_type.rs:23:3
   |
23 |         type Error = u64;
   |         ^^^^

error[E0277]: the trait bound `u32: std::convert::From<std::string::String>` is not satisfied
   --> $DIR/mock_only_one_error_type.rs:15:1
    |
15  | / sp_api::mock_impl_runtime_apis! {
16  | |     impl Api<Block> for MockApi {
17  | |         type Error = u32;
18  | |
...   |
26  | |     }
27  | | }
    | |_^ the trait `std::convert::From<std::string::String>` is not implemented for `u32`
    | 
   ::: $WORKSPACE/primitives/api/src/lib.rs:350:35
    |
350 |       type Error: std::fmt::Debug + From<String>;
    |                                     ------------ required by this bound in `sp_api_hidden_includes_DECL_RUNTIME_APIS::sp_api::ApiErrorExt`
    |
    = help: the following implementations were found:
              <u32 as std::convert::From<bool>>
              <u32 as std::convert::From<char>>
              <u32 as std::convert::From<h2::frame::reason::Reason>>
              <u32 as std::convert::From<h2::frame::reason::Reason>>
            and 18 others
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
