What is the equivalent of jest snapshot testing in Flutter?

Question

Using Jest, a testing library for JS, it is possible to have a \"snapshot\" as followed:

test(\'foo\', () => {
    expect(42).toMatchSnapshot(\"my_snapsho         


        

Answer 1

It is possible for widgets only, using testWidgets:

testWidgets('golden', (tester) async {
  await tester.pumpWidget(Container(
    color: Colors.red,
  ));

  await expectLater(
      find.byType(Container), matchesGoldenFile("red_container.png"));
});

First, you have to pump the widget you want to test (here a red container).

Then you can use matchesGoldenFile combined with expectLater. This will take a screen capture of the widget and compare it to the previously saved capture.

On the first run or when you want to update your goldens, you'll have to pass a flag to flutter test:

flutter test --update-goldens