tests: add tests for local-storage api

frontend/src/lib/utils/storage-types/local-storage.test.ts

@@ -0,0 +1,18 @@
+import { expect, test, vi, describe, beforeEach } from 'vitest';
+import { LocalStorage } from './local-storage';
+import * as environment from '$app/environment';
+
+describe.each([
+	{ isBrowser: true, expectedLocalValue: 'value' },
+	{ isBrowser: false, expectedLocalValue: 'value' }
+])('LocalStorage in environment context', ({ isBrowser, expectedLocalValue }) => {
+	beforeEach(() => {
+		vi.spyOn(environment, 'browser', 'get').mockReturnValue(isBrowser);
+	});
+
+	test(`${isBrowser ? 'browser' : 'server'}: correctly sets and retrieves items`, () => {
+		const storage = new LocalStorage();
+		storage.setItem('test', expectedLocalValue);
+		expect(storage.getItem('test')).toEqual(expectedLocalValue);
+	});
+});

frontend/src/lib/utils/storage-types/local-storage.ts

@@ -1,4 +1,5 @@
 import { browser } from '$app/environment';
+import * as environment from '$app/environment';
 
 export class LocalStorage {
 	#serverSideItems = new Map<string, string>();