diff --git a/src/__tests__/env.test.ts b/src/__tests__/env.test.ts
new file mode 100644
index 0000000..fa03ff5
--- /dev/null
+++ b/src/__tests__/env.test.ts
@@ -0,0 +1,311 @@
+import { validateEnvVariables, requireEnvVariables, getEnv } from '../config/env';
+
+const ENV_KEYS = [
+  'EXPO_PUBLIC_API_BASE_URL',
+  'EXPO_PUBLIC_SOCKET_URL',
+  'EXPO_PUBLIC_APP_ENV',
+  'EXPO_PUBLIC_ENABLE_PUSH_NOTIFICATIONS',
+  'EXPO_PUBLIC_STORYBOOK',
+  'EXPO_PUBLIC_SENTRY_ENABLED',
+];
+
+const savedValues: Record<string, string | undefined> = {};
+
+function setEnv(vars: Record<string, string | undefined>) {
+  for (const key of ENV_KEYS) {
+    savedValues[key] = process.env[key];
+    if (key in vars) {
+      if (vars[key] === undefined) {
+        delete process.env[key];
+      } else {
+        process.env[key] = vars[key];
+      }
+    }
+  }
+}
+
+afterEach(() => {
+  for (const key of ENV_KEYS) {
+    if (savedValues[key] !== undefined) {
+      process.env[key] = savedValues[key];
+    } else {
+      delete process.env[key];
+    }
+  }
+});
+
+describe('validateEnvVariables', () => {
+  it('returns valid when all required vars are present with correct formats', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_APP_ENV: undefined,
+      EXPO_PUBLIC_ENABLE_PUSH_NOTIFICATIONS: undefined,
+      EXPO_PUBLIC_STORYBOOK: undefined,
+      EXPO_PUBLIC_SENTRY_ENABLED: undefined,
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(true);
+    expect(result.message).toBeUndefined();
+  });
+
+  it('returns invalid when EXPO_PUBLIC_API_BASE_URL is missing', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: undefined,
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('EXPO_PUBLIC_API_BASE_URL');
+  });
+
+  it('returns invalid when EXPO_PUBLIC_API_BASE_URL is not https', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'http://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('must use https://');
+  });
+
+  it('returns invalid for completely malformed EXPO_PUBLIC_API_BASE_URL', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'not-a-url',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('Invalid URL');
+  });
+
+  it('returns invalid when EXPO_PUBLIC_SOCKET_URL is missing', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: undefined,
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('EXPO_PUBLIC_SOCKET_URL');
+  });
+
+  it('returns invalid when EXPO_PUBLIC_SOCKET_URL is not ws:// or wss://', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'http://socket.example.com',
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('ws:// or wss://');
+  });
+
+  it('returns valid when EXPO_PUBLIC_SOCKET_URL uses ws://', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'ws://socket.example.com',
+      EXPO_PUBLIC_APP_ENV: undefined,
+      EXPO_PUBLIC_ENABLE_PUSH_NOTIFICATIONS: undefined,
+      EXPO_PUBLIC_STORYBOOK: undefined,
+      EXPO_PUBLIC_SENTRY_ENABLED: undefined,
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(true);
+  });
+
+  it('returns valid when optional EXPO_PUBLIC_APP_ENV is absent', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_APP_ENV: undefined,
+      EXPO_PUBLIC_ENABLE_PUSH_NOTIFICATIONS: undefined,
+      EXPO_PUBLIC_STORYBOOK: undefined,
+      EXPO_PUBLIC_SENTRY_ENABLED: undefined,
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(true);
+  });
+
+  it('returns invalid when EXPO_PUBLIC_APP_ENV has invalid value', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_APP_ENV: 'staging',
+      EXPO_PUBLIC_ENABLE_PUSH_NOTIFICATIONS: undefined,
+      EXPO_PUBLIC_STORYBOOK: undefined,
+      EXPO_PUBLIC_SENTRY_ENABLED: undefined,
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('EXPO_PUBLIC_APP_ENV');
+  });
+
+  it('returns valid when EXPO_PUBLIC_APP_ENV is development', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_APP_ENV: 'development',
+      EXPO_PUBLIC_ENABLE_PUSH_NOTIFICATIONS: undefined,
+      EXPO_PUBLIC_STORYBOOK: undefined,
+      EXPO_PUBLIC_SENTRY_ENABLED: undefined,
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(true);
+  });
+
+  it('returns invalid when EXPO_PUBLIC_ENABLE_PUSH_NOTIFICATIONS is invalid', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_ENABLE_PUSH_NOTIFICATIONS: 'yes',
+      EXPO_PUBLIC_STORYBOOK: undefined,
+      EXPO_PUBLIC_SENTRY_ENABLED: undefined,
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('EXPO_PUBLIC_ENABLE_PUSH_NOTIFICATIONS');
+  });
+
+  it('returns invalid when EXPO_PUBLIC_STORYBOOK has invalid value', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_STORYBOOK: 'maybe',
+      EXPO_PUBLIC_SENTRY_ENABLED: undefined,
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('EXPO_PUBLIC_STORYBOOK');
+  });
+
+  it('returns invalid when EXPO_PUBLIC_SENTRY_ENABLED has invalid value', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_SENTRY_ENABLED: 'on',
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('EXPO_PUBLIC_SENTRY_ENABLED');
+  });
+
+  it('returns invalid for both missing required vars', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: undefined,
+      EXPO_PUBLIC_SOCKET_URL: undefined,
+    });
+
+    const result = validateEnvVariables();
+    expect(result.valid).toBe(false);
+    expect(result.message).toContain('EXPO_PUBLIC_API_BASE_URL');
+    expect(result.message).toContain('EXPO_PUBLIC_SOCKET_URL');
+  });
+});
+
+describe('requireEnvVariables', () => {
+  it('returns config object when all required vars are valid', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_APP_ENV: undefined,
+    });
+
+    const config = requireEnvVariables();
+    expect(config.EXPO_PUBLIC_API_BASE_URL).toBe('https://api.example.com');
+    expect(config.EXPO_PUBLIC_SOCKET_URL).toBe('wss://socket.example.com');
+  });
+
+  it('throws when required vars are missing', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: undefined,
+      EXPO_PUBLIC_SOCKET_URL: undefined,
+    });
+
+    expect(() => requireEnvVariables()).toThrow('Environment Configuration Error');
+  });
+
+  it('throws when URL formats are invalid', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'http://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'not-ws',
+    });
+
+    expect(() => requireEnvVariables()).toThrow('Environment Configuration Error');
+  });
+
+  it('defaults EXPO_PUBLIC_APP_ENV to development when not production', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_APP_ENV: undefined,
+    });
+
+    const config = requireEnvVariables();
+    expect(config.EXPO_PUBLIC_APP_ENV).toBe('development');
+  });
+
+  it('sets EXPO_PUBLIC_APP_ENV to production when explicitly set', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+      EXPO_PUBLIC_APP_ENV: 'production',
+    });
+
+    const config = requireEnvVariables();
+    expect(config.EXPO_PUBLIC_APP_ENV).toBe('production');
+  });
+});
+
+describe('getEnv', () => {
+  it('returns value for EXPO_PUBLIC_API_BASE_URL', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+    });
+
+    expect(getEnv('EXPO_PUBLIC_API_BASE_URL')).toBe('https://api.example.com');
+  });
+
+  it('returns value for EXPO_PUBLIC_SOCKET_URL', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+    });
+
+    expect(getEnv('EXPO_PUBLIC_SOCKET_URL')).toBe('wss://socket.example.com');
+  });
+
+  it('throws when EXPO_PUBLIC_API_BASE_URL is missing', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: undefined,
+      EXPO_PUBLIC_SOCKET_URL: 'wss://socket.example.com',
+    });
+
+    expect(() => getEnv('EXPO_PUBLIC_API_BASE_URL')).toThrow(
+      'Environment variable EXPO_PUBLIC_API_BASE_URL is not set'
+    );
+  });
+
+  it('throws when EXPO_PUBLIC_SOCKET_URL is missing', () => {
+    setEnv({
+      EXPO_PUBLIC_API_BASE_URL: 'https://api.example.com',
+      EXPO_PUBLIC_SOCKET_URL: undefined,
+    });
+
+    expect(() => getEnv('EXPO_PUBLIC_SOCKET_URL')).toThrow(
+      'Environment variable EXPO_PUBLIC_SOCKET_URL is not set'
+    );
+  });
+});
diff --git a/src/__tests__/linkingConfig.test.ts b/src/__tests__/linkingConfig.test.ts
new file mode 100644
index 0000000..545f425
--- /dev/null
+++ b/src/__tests__/linkingConfig.test.ts
@@ -0,0 +1,240 @@
+import * as Linking from 'expo-linking';
+import * as Notifications from 'expo-notifications';
+
+import { linking, buildScreenUrl, setDeepLinkAnalyticsHandler } from '../navigation/linking';
+import { NotificationType } from '../types/notifications';
+
+jest.mock('../utils/logger', () => ({
+  info: jest.fn(),
+  warn: jest.fn(),
+  error: jest.fn(),
+  default: {
+    info: jest.fn(),
+    warn: jest.fn(),
+    error: jest.fn(),
+    infoSync: jest.fn(),
+    warnSync: jest.fn(),
+    errorSync: jest.fn(),
+    debugSync: jest.fn(),
+  },
+}));
+
+jest.mock('expo-notifications', () => ({
+  getLastNotificationResponseAsync: jest.fn(() => Promise.resolve(null)),
+  addNotificationResponseReceivedListener: jest.fn(() => ({ remove: jest.fn() })),
+  addNotificationReceivedListener: jest.fn(() => ({ remove: jest.fn() })),
+}));
+
+jest.mock('expo-linking', () => ({
+  createURL: jest.fn((path: string) => `teachlink://${path}`),
+  addEventListener: jest.fn(() => ({ remove: jest.fn() })),
+  getInitialURL: jest.fn(() => Promise.resolve(null)),
+}));
+
+beforeEach(() => {
+  jest.clearAllMocks();
+  setDeepLinkAnalyticsHandler(null);
+});
+
+describe('linking config', () => {
+  describe('prefixes', () => {
+    it('includes the custom scheme and web URLs', () => {
+      expect(linking.prefixes).toContain('teachlink://');
+      expect(linking.prefixes).toContain('https://teachlink.com');
+      expect(linking.prefixes).toContain('https://www.teachlink.com');
+    });
+  });
+
+  describe('getInitialURL', () => {
+    it('returns null when no notification and no external URL', async () => {
+      (Notifications.getLastNotificationResponseAsync as jest.Mock).mockResolvedValue(null);
+      (Linking.getInitialURL as jest.Mock).mockResolvedValue(null);
+
+      const url = await linking.getInitialURL!();
+      expect(url).toBeNull();
+    });
+
+    it('returns notification deep link when notification response exists', async () => {
+      (Notifications.getLastNotificationResponseAsync as jest.Mock).mockResolvedValue({
+        notification: {
+          request: {
+            content: {
+              data: {
+                type: NotificationType.COURSE_UPDATE,
+                courseId: '456',
+              },
+            },
+          },
+        },
+      });
+
+      const url = await linking.getInitialURL!();
+      expect(url).toBe('teachlink://course/456');
+    });
+
+    it('returns external URL when no notification response', async () => {
+      (Notifications.getLastNotificationResponseAsync as jest.Mock).mockResolvedValue(null);
+      (Linking.getInitialURL as jest.Mock).mockResolvedValue('teachlink://messages/789');
+
+      const url = await linking.getInitialURL!();
+      expect(url).toBe('teachlink://messages/789');
+    });
+
+    it('handles malformed notification data gracefully', async () => {
+      (Notifications.getLastNotificationResponseAsync as jest.Mock).mockResolvedValue({
+        notification: {
+          request: {
+            content: {
+              data: null,
+            },
+          },
+        },
+      });
+      (Linking.getInitialURL as jest.Mock).mockResolvedValue(null);
+
+      const url = await linking.getInitialURL!();
+      expect(url).toBeNull();
+    });
+
+    it('handles notification with missing type field', async () => {
+      (Notifications.getLastNotificationResponseAsync as jest.Mock).mockResolvedValue({
+        notification: {
+          request: {
+            content: {
+              data: { courseId: '999' },
+            },
+          },
+        },
+      });
+      (Linking.getInitialURL as jest.Mock).mockResolvedValue(null);
+
+      const url = await linking.getInitialURL!();
+      expect(url).toBeNull();
+    });
+  });
+
+  describe('subscribe', () => {
+    it('returns a cleanup function', () => {
+      const cleanup = linking.subscribe!(jest.fn());
+      expect(typeof cleanup).toBe('function');
+    });
+
+    it('calls listener when linking event fires', () => {
+      const listener = jest.fn();
+      const urlHandler = jest.fn();
+
+      (Linking.addEventListener as jest.Mock).mockImplementation((_event: string, handler: any) => {
+        urlHandler.mockImplementation(handler);
+        return { remove: jest.fn() };
+      });
+
+      const cleanup = linking.subscribe!(listener);
+      urlHandler({ url: 'teachlink://course/123' });
+
+      expect(listener).toHaveBeenCalledWith('teachlink://course/123');
+      cleanup();
+    });
+
+    it('calls listener when notification response is received', () => {
+      const listener = jest.fn();
+      const responseHandler = jest.fn();
+
+      (Notifications.addNotificationResponseReceivedListener as jest.Mock).mockImplementation(
+        (handler: any) => {
+          responseHandler.mockImplementation(handler);
+          return { remove: jest.fn() };
+        }
+      );
+
+      const cleanup = linking.subscribe!(listener);
+      responseHandler({
+        notification: {
+          request: {
+            content: {
+              data: {
+                type: NotificationType.MESSAGE,
+                conversationId: 'conv-42',
+              },
+            },
+          },
+        },
+      });
+
+      expect(listener).toHaveBeenCalledWith('teachlink://messages/conv-42');
+      cleanup();
+    });
+
+    it('calls listener for foreground notifications', () => {
+      const listener = jest.fn();
+      const foregroundHandler = jest.fn();
+
+      (Notifications.addNotificationReceivedListener as jest.Mock).mockImplementation(
+        (handler: any) => {
+          foregroundHandler.mockImplementation(handler);
+          return { remove: jest.fn() };
+        }
+      );
+
+      const cleanup = linking.subscribe!(listener);
+      foregroundHandler({
+        request: {
+          content: {
+            data: {
+              type: NotificationType.LEARNING_REMINDER,
+            },
+          },
+        },
+      } as any);
+
+      expect(listener).toHaveBeenCalledWith('teachlink://learn');
+      cleanup();
+    });
+  });
+});
+
+describe('buildScreenUrl', () => {
+  it('builds URL for CourseDetail with courseId', () => {
+    const url = buildScreenUrl('CourseDetail', { courseId: '123' });
+    expect(url).toBe('teachlink://course/123');
+  });
+
+  it('builds URL for Chat with conversationId', () => {
+    const url = buildScreenUrl('Chat', { conversationId: 'conv-789' });
+    expect(url).toBe('teachlink://messages/conv-789');
+  });
+
+  it('builds URL for AchievementDetail', () => {
+    const url = buildScreenUrl('AchievementDetail', { achievementId: 'ach-1' });
+    expect(url).toBe('teachlink://achievements/ach-1');
+  });
+
+  it('builds URL for CommunityPost', () => {
+    const url = buildScreenUrl('CommunityPost', { postId: 'post-5' });
+    expect(url).toBe('teachlink://community/post-5');
+  });
+
+  it('builds URL for tab screens without params', () => {
+    expect(buildScreenUrl('Home')).toBe('teachlink://');
+    expect(buildScreenUrl('Courses')).toBe('teachlink://courses');
+    expect(buildScreenUrl('Messages')).toBe('teachlink://messages');
+    expect(buildScreenUrl('Learning')).toBe('teachlink://learn');
+    expect(buildScreenUrl('Community')).toBe('teachlink://community');
+    expect(buildScreenUrl('Settings')).toBe('teachlink://settings');
+  });
+
+  it('encodes special characters in params', () => {
+    const url = buildScreenUrl('CourseDetail', { courseId: 'a b&c=d' });
+    expect(url).toBe('teachlink://course/a%20b%26c%3Dd');
+  });
+
+  it('does not crash with XSS payload in params', () => {
+    const url = buildScreenUrl('CourseDetail', { courseId: '<script>alert(1)</script>' });
+    expect(url).toContain('teachlink://course/');
+    expect(url).not.toContain('<script>');
+  });
+
+  it('handles empty string param value', () => {
+    const url = buildScreenUrl('CourseDetail', { courseId: '' });
+    expect(url).toBe('teachlink://course/');
+  });
+});