Dart Interface Based Mocking

main.dart

import "dart:async";

class LoginRequest {}

class LoginResponse {
  String code;
  LoginResponse(this.code);
}

class LogoutRequest {}

class LogoutResponse {}

class APIError {
  String message;
  num code;

  APIError(this.message, this.code);
}

var InternalError = APIError("This is a sample internal error", 500);

class IServerAPI {
  Future<LoginResponse> Login(LoginRequest req) {
    return null;
  }

  Future<LogoutResponse> LogOut(LogoutRequest req) {
    return null;
  }
}

class SuccessServerAPI implements IServerAPI {
  @override
  Future<LogoutResponse> LogOut(LogoutRequest req) {
    return Future.value(LogoutResponse());
  }

  @override
  Future<LoginResponse> Login(LoginRequest req) {
    return Future.value(LoginResponse("this is the code"));
  }
}

class LoginErrorAPI implements IServerAPI {
  @override
  Future<LogoutResponse> LogOut(LogoutRequest req) {
    return Future.value(LogoutResponse());
  }

  @override
  Future<LoginResponse> Login(LoginRequest req) {
    return Future.error(InternalError);
  }
}

class SlowAPI implements IServerAPI {
  @override
  Future<LogoutResponse> LogOut(LogoutRequest req) async {
    await Future.delayed(const Duration(seconds: 1), () {
      print("delay complete");
    });
    return Future.value(LogoutResponse());
  }

  @override
  Future<LoginResponse> Login(LoginRequest req) async {
    await Future.delayed(const Duration(seconds: 1), () {
      print("delay complete");
    });
    return Future.value(LoginResponse("200"));
  }
}

void main() async {
  IServerAPI api = SuccessServerAPI();

  var inRes = await api.Login(LoginRequest());

  print(inRes.code);

  var outRes = await api.LogOut(LogoutRequest());

  print(outRes);

  api = LoginErrorAPI();

  try {
    inRes = await api.Login(LoginRequest());
    print(inRes);
  } on APIError catch (err) {
    print(err.message + " " + err.code.toString());
  } catch (e) {
    print(e);
  }
  api = SlowAPI();
  try {
    inRes = await api.Login(LoginRequest());
    print(inRes);
    outRes = await api.LogOut(LogoutRequest());
    print(outRes);
  } on APIError catch (err) {
    print(err.message + " " + err.code.toString());
  } catch (e) {
    print(e);
  }
}