How to testing main.dart

main.dart

int sumInt(int a, int b) {
  return a + b;
}
int main(List<String> args) {
  var result;
  var a = 10;

  result = sumInt(a, 50);
  return result;
}

gao.dart

int calculate() {
  return 6 +10;
}

gao_test.dart

import 'package:gao/gao.dart';
import 'package:test/test.dart';

void main() {
  test("test to check add method", () {
    expect(calculate, result );
  });
}

The question is How I testing main.dart.So I think import main.dart in gao_test.dart but it was error import.Please help me.