feat: add theme cubit

lib/character_themes/character_theme.dart

@@ -3,6 +3,9 @@ import 'package:flame/palette.dart';
 
 /// {@template character_theme}
 /// Template for creating character themes.
+///
+/// Any character specific game pieces should have a getter specified here so
+/// their corresponding assets can be retrieved for the game.
 /// {@endtemplate}
 abstract class CharacterTheme extends Equatable {
   /// {@macro character_theme}

lib/character_themes/cubit/theme_cubit.dart

@@ -0,0 +1,13 @@
+import 'package:bloc/bloc.dart';
+import 'package:equatable/equatable.dart';
+import 'package:pinball/character_themes/character_themes.dart';
+
+part 'theme_state.dart';
+
+class ThemeCubit extends Cubit<ThemeState> {
+  ThemeCubit() : super(const ThemeState(DashTheme()));
+
+  void themeSelected(CharacterTheme theme) {
+    emit(ThemeState(theme));
+  }
+}

lib/character_themes/cubit/theme_state.dart

@@ -0,0 +1,10 @@
+part of 'theme_cubit.dart';
+
+class ThemeState extends Equatable {
+  const ThemeState(this.theme);
+
+  final CharacterTheme theme;
+
+  @override
+  List<Object> get props => [theme];
+}

test/character_themes/cubit/theme_cubit_test.dart

@@ -0,0 +1,23 @@
+import 'package:bloc_test/bloc_test.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pinball/character_themes/character_themes.dart';
+
+void main() {
+  group('ThemeCubit', () {
+    test('initial state has Dash theme', () {
+      final themeCubit = ThemeCubit();
+      expect(themeCubit.state.theme, equals(const DashTheme()));
+    });
+
+    group('themeSelected', () {
+      blocTest<ThemeCubit, ThemeState>(
+        'emits selected theme',
+        build: ThemeCubit.new,
+        act: (bloc) => bloc.themeSelected(const SparkyTheme()),
+        expect: () => [
+          const ThemeState(SparkyTheme()),
+        ],
+      );
+    });
+  });
+}

test/character_themes/cubit/theme_state_test.dart

@@ -0,0 +1,19 @@
+// ignore_for_file: prefer_const_constructors
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pinball/character_themes/character_themes.dart';
+
+void main() {
+  group('ThemeState', () {
+    test('can be instantiated', () {
+      expect(const ThemeState(DashTheme()), isNotNull);
+    });
+
+    test('supports value equality', () {
+      expect(
+        ThemeState(DashTheme()),
+        equals(const ThemeState(DashTheme())),
+      );
+    });
+  });
+}