dart_test: how to execute `setUp` if a loop before `test` is used based on the data assigned in `setUp`?

The problem is in this code:

void main() {
  late List<int> data;

  setUp(() async {
    data = [11, 22, 33];
  });
  
  int counter = 0;
  for (final d in data) { // error
    test('data', () {
      expect(d, data[counter++]);
    });
  }
}

error:

Local 'data' has not been initialized.

How can we specify that the setUp function should be called before the data is used?

I tried wrapping test in group - same error.

After two days of agony, I found an optimal solution that allows you to use collection sets and call setUp and tearDown exactly at test time.

Look, here's a simple wrapper:

@isTest
Future<void> testWith(
  Object description,
  dynamic Function() body, {
  dynamic Function()? setUp,
  dynamic Function()? tearDown,
}) async {
  test(description, () async {
    await setUp?.call();
    await body.call();
    await tearDown?.call();
  });
}

Add the desired parameters as needed. Also everything can be asynchronous and work fine.

Now we can execute this code (slightly expanded to demonstrate the capabilities):

Future<void> main() async {
  late List<int> data;
  Future<void> setUpAction() async {
    print('setUpAction');
    data = [11, 22, 33];
  }

  Future<void> tearDownAction() async {
    print('tearDownAction');
    data = [];
  }

  await testWith(
    'Test_1 data',
    setUp: setUpAction,
    tearDown: tearDownAction,
    () {
      int counter = 0;
      for (final d in data) {
        print('test_1: $d');
        expect(d, data[counter++]);
      }
    },
  );

  await testWith(
    'Test_2 data',
    setUp: setUpAction,
    tearDown: tearDownAction,
    () {
      int counter = 0;
      for (final d in data.take(2)) {
        print('test_1: $d');
        expect(d, data[counter++]);
      }
    },
  );
}

The output to the console is as follows:

setUpAction
test_1: 11
test_1: 22
test_1: 33
tearDownAction
setUpAction
test_1: 11
test_1: 22
tearDownAction

If we use the setUpAction from this answer, we get two problems:

• calling setUpAction will happen twice and we will be testing not exactly what is intended
• there is no possibility to use multiple tests, because all tests are collected into a list and only then start executing. The point has been demonstrated here.

Add the isTest annotation so idea can see your tests (if necessary, there is also an isTestGroup annotation) from package meta:

Used to annotate a test framework function that runs a single test. Tools, such as IDEs, can show invocations of such function in a file structure view to help the user navigating in large test files. The first parameter of the function must be the description of the test.