test: added test for all files under utils/themes

Author: rohansen856

test/utils/themes/dark_theme_test.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:taskwarrior/app/utils/themes/dark_theme.dart';
+
+void main() {
+  group('darkTheme', () {
+    test('darkTheme has correct brightness', () {
+      expect(darkTheme.brightness, Brightness.dark);
+    });
+  });
+}

test/utils/themes/light_theme_test.dart

@@ -0,0 +1,11 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:taskwarrior/app/utils/themes/light_theme.dart';
+
+void main() {
+  group('lightTheme', () {
+    test('lightTheme has correct brightness', () {
+      expect(lightTheme.brightness, Brightness.light);
+    });
+  });
+}