Add E2E test for settings and locale detection

Partially resolves: Add unit tests #33

cypress.config.ts

@@ -0,0 +1,17 @@
+import { defineConfig } from "cypress";
+
+export default defineConfig({
+  component: {
+    devServer: {
+      framework: "next",
+      bundler: "webpack",
+    },
+  },
+
+  e2e: {
+    baseUrl: "http://localhost:3000",
+    setupNodeEvents(on, config) {
+      // implement node event listeners here
+    },
+  },
+});

cypress/e2e/locale.cy.ts

@@ -0,0 +1,76 @@
+describe('Locale detection', () => {
+	beforeEach(() => {
+		cy.intercept('/api/locales', {
+			fixture: 'locales.json',
+		});
+
+		cy.clearAllCookies();
+		cy.clearAllLocalStorage();
+	});
+
+	it('English locale detection', () => {
+		cy
+			.intercept('/api/articles?locale=en&metadataOnly=true', {
+				fixture: 'articles.json',
+			})
+			.as('getArticles');
+		cy.visit('/en').intercept('/en').as('page'); // Visit the English homepage
+
+		cy.url().should('include', '/en'); // Check that the URL contains the locale
+
+		cy.getCookie('NEXT_LOCALE').should('have.property', 'value', 'en'); // Check that the locale cookie is set to English
+
+		cy.wait('@getArticles'); // Wait for the locale to be set
+		cy
+			.window()
+			.its('localStorage')
+			.then((localStorage) => {
+				expect(localStorage.getItem('settings')).exist;
+
+				const settings = JSON.parse(localStorage.getItem('settings') || '{}');
+
+				expect(settings.locale).to.equal('en'); // Check that the locale in the settings is set to English
+			});
+
+		cy
+			.title()
+			.should('eq', 'Survival Manual'); // Check that the title is in English
+
+		cy
+			.get('h1')
+			.should('have.text', 'Introduction'); // Check that the text is in English
+	});
+
+	it('Ukrainian locale detection', () => {
+		cy
+			.intercept('/api/articles?locale=uk&metadataOnly=true', {
+				fixture: 'articles.uk.json',
+			})
+			.as('getArticles');
+		cy.visit('/uk'); // Visit the Ukrainian homepage
+
+		cy.url().should('include', '/uk'); // Check that the URL contains the locale
+
+		cy.getCookie('NEXT_LOCALE').should('have.property', 'value', 'uk'); // Check that the locale cookie is set to Ukrainian
+
+		cy.wait('@getArticles'); // Wait for the locale to be set
+		cy
+			.window()
+			.its('localStorage')
+			.then((localStorage) => {
+				expect(localStorage.getItem('settings')).exist;
+
+				const settings = JSON.parse(localStorage.getItem('settings') || '{}');
+
+				expect(settings.locale).to.equal('uk'); // Check that the locale in the settings is set to English
+			});
+
+		cy
+			.title()
+			.should('eq', 'Довідник по виживанню'); // Check that the title is in Ukrainian
+
+		cy
+			.get('h1')
+			.should('have.text', 'Знайомство'); // Check that the text is in Ukrainian
+	});
+});