test: included ContactBehavior tests

packages/pinball_flame/lib/src/contact_behavior.dart

@@ -3,19 +3,21 @@ import 'package:flame_forge2d/flame_forge2d.dart';
 import 'package:flutter/material.dart';
 import 'package:pinball_flame/pinball_flame.dart';
 
-/// Adds a new [ContactCallbacks] to the parent.
+/// Appends a new [ContactCallbacks] to the parent.
 ///
 /// This is a convenience class for adding a [ContactCallbacks] to the parent.
-/// In constract with just adding a [ContactCallbacks] to the parent's userData,
-/// this class respects the previous [ContactCallbacks] in the parent's
-/// userData, if any. Hence, it avoids overriding any previous
+/// In constract with just adding a [ContactCallbacks] to the parent's body
+/// userData, this class respects the previous [ContactCallbacks] in the
+/// parent's body userData, if any. Hence, it avoids overriding any previous
 /// [ContactCallbacks] in the parent.
 ///
 /// It does so by grouping the [ContactCallbacks] in a [_ContactCallbacksGroup],
 /// and resetting the parent's userData accordingly.
 // TODO(alestiago): Make use of generics to infer the type of the contact.
 // https://github.com/VGVentures/pinball/pull/234#discussion_r859182267
-abstract class ContactBehavior<T extends BodyComponent> extends Component
+// TODO(alestiago): Consider if there is a need to support adjusting a fixture's
+// userData.
+class ContactBehavior<T extends BodyComponent> extends Component
     with ContactCallbacks, ParentIsA<T> {
   @override
   @mustCallSuper

packages/pinball_flame/test/src/contact_behavior_test.dart

@@ -0,0 +1,155 @@
+// ignore_for_file: cascade_invocations
+
+import 'package:flame_forge2d/flame_forge2d.dart';
+import 'package:flame_test/flame_test.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:mocktail/mocktail.dart';
+import 'package:pinball_flame/pinball_flame.dart';
+
+class _TestBodyComponent extends BodyComponent {
+  @override
+  Body createBody() {
+    return world.createBody(BodyDef());
+  }
+}
+
+class _TestContactBehavior extends ContactBehavior {
+  int beginContactCallsCount = 0;
+  @override
+  void beginContact(Object other, Contact contact) {
+    beginContactCallsCount++;
+    super.beginContact(other, contact);
+  }
+
+  int endContactCallsCount = 0;
+  @override
+  void endContact(Object other, Contact contact) {
+    endContactCallsCount++;
+    super.endContact(other, contact);
+  }
+
+  int preSolveContactCallsCount = 0;
+  @override
+  void preSolve(Object other, Contact contact, Manifold oldManifold) {
+    preSolveContactCallsCount++;
+    super.preSolve(other, contact, oldManifold);
+  }
+
+  int postSolveContactCallsCount = 0;
+  @override
+  void postSolve(Object other, Contact contact, ContactImpulse impulse) {
+    postSolveContactCallsCount++;
+    super.postSolve(other, contact, impulse);
+  }
+}
+
+class _MockContactCallbacks extends Mock implements ContactCallbacks {}
+
+class _MockContact extends Mock implements Contact {}
+
+class _MockManifold extends Mock implements Manifold {}
+
+class _MockContactImpulse extends Mock implements ContactImpulse {}
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  final flameTester = FlameTester(Forge2DGame.new);
+
+  group('ContactBehavior', () {
+    late Object other;
+    late Contact contact;
+    late Manifold manifold;
+    late ContactImpulse contactImpulse;
+
+    setUp(() {
+      other = Object();
+      contact = _MockContact();
+      manifold = _MockManifold();
+      contactImpulse = _MockContactImpulse();
+    });
+
+    flameTester.test(
+      'should add a new ContactCallbacks to the parent',
+      (game) async {
+        final parent = _TestBodyComponent();
+        final contactBehavior = ContactBehavior();
+        await parent.add(contactBehavior);
+        await game.ensureAdd(parent);
+
+        expect(parent.body.userData, contactBehavior);
+      },
+    );
+
+    flameTester.test(
+      "should respect the previous ContactCallbacks in the parent's userData",
+      (game) async {
+        final parent = _TestBodyComponent();
+        await game.ensureAdd(parent);
+        final contactCallbacks1 = _MockContactCallbacks();
+        parent.body.userData = contactCallbacks1;
+
+        final contactBehavior = ContactBehavior();
+        await parent.ensureAdd(contactBehavior);
+
+        final contactCallbacks = parent.body.userData! as ContactCallbacks;
+
+        contactCallbacks.beginContact(other, contact);
+        verify(
+          () => contactCallbacks1.beginContact(other, contact),
+        ).called(1);
+
+        contactCallbacks.endContact(other, contact);
+        verify(
+          () => contactCallbacks1.endContact(other, contact),
+        ).called(1);
+
+        contactCallbacks.preSolve(other, contact, manifold);
+        verify(
+          () => contactCallbacks1.preSolve(other, contact, manifold),
+        ).called(1);
+
+        contactCallbacks.postSolve(other, contact, contactImpulse);
+        verify(
+          () => contactCallbacks1.postSolve(other, contact, contactImpulse),
+        ).called(1);
+      },
+    );
+
+    flameTester.test('can group multiple ContactBehaviors and keep listening',
+        (game) async {
+      final parent = _TestBodyComponent();
+      await game.ensureAdd(parent);
+
+      final contactBehavior1 = _TestContactBehavior();
+      final contactBehavior2 = _TestContactBehavior();
+      final contactBehavior3 = _TestContactBehavior();
+      await parent.ensureAddAll([
+        contactBehavior1,
+        contactBehavior2,
+        contactBehavior3,
+      ]);
+
+      final contactCallbacks = parent.body.userData! as ContactCallbacks;
+
+      contactCallbacks.beginContact(other, contact);
+      expect(contactBehavior1.beginContactCallsCount, equals(1));
+      expect(contactBehavior2.beginContactCallsCount, equals(1));
+      expect(contactBehavior3.beginContactCallsCount, equals(1));
+
+      contactCallbacks.endContact(other, contact);
+      expect(contactBehavior1.endContactCallsCount, equals(1));
+      expect(contactBehavior2.endContactCallsCount, equals(1));
+      expect(contactBehavior3.endContactCallsCount, equals(1));
+
+      contactCallbacks.preSolve(other, contact, manifold);
+      expect(contactBehavior1.preSolveContactCallsCount, equals(1));
+      expect(contactBehavior2.preSolveContactCallsCount, equals(1));
+      expect(contactBehavior3.preSolveContactCallsCount, equals(1));
+
+      contactCallbacks.postSolve(other, contact, contactImpulse);
+      expect(contactBehavior1.postSolveContactCallsCount, equals(1));
+      expect(contactBehavior2.postSolveContactCallsCount, equals(1));
+      expect(contactBehavior3.postSolveContactCallsCount, equals(1));
+    });
+  });
+}