The Three Rules of TDD in Dart

a-test-1.dart

// T1 – Empty test (Rule 3)

import 'package:test/test.dart';
import 'b-production-1.dart';

main() {
  
}

b-production-1.dart

// P1 – Empty production file (Rule 1)

c-test-2.dart

// T2 – (Rule 2)

import 'package:test/test.dart';
import 'd-production-2.dart';

main() {
  test('it works', () {
    doStuff(); // NoSuchMethodError – time to implement the function (Rule 2)
  });
}

d-production-2.dart

// P2 – (Rule 3)

doStuff() {} // Analyzer is happy. Time to return to test (Rule 1)

e-test-3.dart

// T3 – (Rule 2)

import 'package:test/test.dart';
import 'f-production-3.dart';

main() {
  test('it works', () {
    expect(doStuff(), 'some value'); // Fails: <null != 'some value'> Time to implement (Rule 2)
  });
}

f-production-3.dart

// P3 – (Rule 3)

doStuff() {
  return 'some value'; // Test passes, return to test. (Rule 1)
}