halkyon/halkyon_learn_flutter/test/feature/profile/avatar_image_test.dart

import 'dart:typed_data';
import 'dart:ui' as ui;

import 'package:flutter_test/flutter_test.dart';
import 'package:halkyon_learn_flutter/src/feature/profile/data/avatar_image.dart';

/// A PNG [width] × [height], red on its left half, blue on its right.
Future<Uint8List> picture(int width, int height) async {
  final recorder = ui.PictureRecorder();
  ui.Canvas(recorder)
    ..drawRect(
      ui.Rect.fromLTWH(0, 0, width / 2, height.toDouble()),
      ui.Paint()..color = const ui.Color(0xFFFF0000),
    )
    ..drawRect(
      ui.Rect.fromLTWH(width / 2, 0, width / 2, height.toDouble()),
      ui.Paint()..color = const ui.Color(0xFF0000FF),
    );
  final image = await recorder.endRecording().toImage(width, height);
  final png = await image.toByteData(format: ui.ImageByteFormat.png);
  return png!.buffer.asUint8List();
}

Future<ui.Image> decoded(Uint8List png) async {
  final codec = await ui.instantiateImageCodec(png);
  return (await codec.getNextFrame()).image;
}

void main() {
  TestWidgetsFlutterBinding.ensureInitialized();

  test('a picture becomes its middle square, at most 400 pixels a side, as '
      'a PNG', () async {
    final wide = await avatarPng(await picture(1200, 600));
    final image = await decoded(wide);

    expect((image.width, image.height), (400, 400));
    expect(wide.sublist(0, 8), [
      0x89,
      0x50,
      0x4e,
      0x47,
      0x0d,
      0x0a,
      0x1a,
      0x0a,
    ]);
    // The middle square of a picture red and blue side by side holds both.
    final pixels = (await image.toByteData())!;
    expect(pixels.getUint8(0), greaterThan(200));
    expect(pixels.getUint8(399 * 4 + 2), greaterThan(200));
  });

  test('a small picture keeps its size', () async {
    final image = await decoded(await avatarPng(await picture(100, 160)));

    expect((image.width, image.height), (100, 100));
  });

  test('what is no picture is refused', () async {
    await expectLater(
      avatarPng(Uint8List.fromList([1, 2, 3])),
      throwsA(anything),
    );
  });
}