I have just one little idea how to improve readability of this code:

add to the given section:

```dart
var jozef = new Data.fromMap({'id': 47, 'name': 'jozef'});
var anicka = new Data.fromMap({'id': 49, 'name': 'anicka'});
```

when section becomes:

```dart
collection.add(jozef);
collection.add(anicka);
```

And you can change then section to:

```dart
  expect(event.removedItems.isEmpty, isTrue);
  expect(event.changedItems.isEmpty, isTrue);
  expect(event.addedItems, equals([jozef]));
  expect(filteredData, unorderedEquals([data[11], data[12], jozef]);
```