diff --git a/__tests__/users.test.ts b/__tests__/users.test.ts
index 38bd93e..30a9031 100644
--- a/__tests__/users.test.ts
+++ b/__tests__/users.test.ts
@@ -1,7 +1,6 @@
 /**
  * Test suite for Users API
- * This test file will fail due to the TypeError bug in api/users.ts
- * Used for Workflow #1 - Bug Fixing
+ * Comprehensive unit tests with edge cases and error handling
  */
 
 import { getUserById, getUserEmail, isAdmin, formatUserName } from '../api/users';
@@ -11,14 +10,36 @@ describe('Users API', () => {
     it('should return a user when given a valid ID', () => {
       const user = getUserById(1);
       expect(user).toBeDefined();
-      expect(user.name).toBe('Alice Johnson');
+      expect(user?.name).toBe('Alice Johnson');
+      expect(user?.id).toBe(1);
+      expect(user?.email).toBe('alice@example.com');
+      expect(user?.role).toBe('admin');
     });
 
-    // This test will FAIL due to the bug!
     it('should handle non-existent user ID gracefully', () => {
       const user = getUserById(999);
       expect(user).toBeUndefined();
     });
+
+    it('should return correct user for each valid ID', () => {
+      const user2 = getUserById(2);
+      expect(user2?.name).toBe('Bob Smith');
+      expect(user2?.role).toBe('user');
+
+      const user3 = getUserById(3);
+      expect(user3?.name).toBe('Charlie Brown');
+      expect(user3?.role).toBe('guest');
+    });
+
+    it('should handle negative ID values', () => {
+      const user = getUserById(-1);
+      expect(user).toBeUndefined();
+    });
+
+    it('should handle zero as ID', () => {
+      const user = getUserById(0);
+      expect(user).toBeUndefined();
+    });
   });
 
   describe('getUserEmail', () => {
@@ -27,10 +48,24 @@ describe('Users API', () => {
       expect(email).toBe('bob@example.com');
     });
 
-    // This test will FAIL - TypeError!
-    it('should handle non-existent user', () => {
+    it('should return email for admin user', () => {
+      const email = getUserEmail(1);
+      expect(email).toBe('alice@example.com');
+    });
+
+    it('should return undefined for non-existent user', () => {
+      const email = getUserEmail(999);
+      expect(email).toBeUndefined();
+    });
+
+    it('should not throw error for invalid user ID', () => {
       expect(() => getUserEmail(999)).not.toThrow();
     });
+
+    it('should handle negative user IDs', () => {
+      const email = getUserEmail(-5);
+      expect(email).toBeUndefined();
+    });
   });
 
   describe('isAdmin', () => {
@@ -42,10 +77,21 @@ describe('Users API', () => {
       expect(isAdmin(2)).toBe(false);
     });
 
-    // This test will FAIL - TypeError!
-    it('should handle non-existent user', () => {
+    it('should return false for guest user', () => {
+      expect(isAdmin(3)).toBe(false);
+    });
+
+    it('should return false for non-existent user', () => {
+      expect(isAdmin(999)).toBe(false);
+    });
+
+    it('should not throw error when checking non-existent user', () => {
       expect(() => isAdmin(999)).not.toThrow();
     });
+
+    it('should return false for negative user IDs', () => {
+      expect(isAdmin(-1)).toBe(false);
+    });
   });
 
   describe('formatUserName', () => {
@@ -53,5 +99,22 @@ describe('Users API', () => {
       const user = { id: 1, name: 'john doe', email: 'john@test.com', role: 'user' as const };
       expect(formatUserName(user)).toBe('JOHN DOE');
     });
+
+    it('should format existing user names correctly', () => {
+      const user1 = getUserById(1);
+      if (user1) {
+        expect(formatUserName(user1)).toBe('ALICE JOHNSON');
+      }
+    });
+
+    it('should handle single-word names', () => {
+      const user = { id: 5, name: 'Alice', email: 'alice@test.com', role: 'admin' as const };
+      expect(formatUserName(user)).toBe('ALICE');
+    });
+
+    it('should handle names with special characters', () => {
+      const user = { id: 6, name: "O'Brien", email: 'obrien@test.com', role: 'user' as const };
+      expect(formatUserName(user)).toBe("O'BRIEN");
+    });
   });
 });
\ No newline at end of file
diff --git a/api/users.ts b/api/users.ts
index 45a29e0..1512a52 100644
--- a/api/users.ts
+++ b/api/users.ts
@@ -20,47 +20,42 @@ const users: User[] = [
 
 /**
  * Get user by ID
- * BUG: This function doesn't handle the case when user is not found
+ * @param id - The user ID to search for
+ * @returns The user object if found, undefined otherwise
  */
-export function getUserById(id: number): User {
+export function getUserById(id: number): User | undefined {
   const user = users.find(u => u.id === id);
-  // TypeError will occur here when user is undefined
   return user;
 }
 
 /**
  * Get user's email
- * BUG: Accessing property on potentially undefined result
+ * @param userId - The user ID
+ * @returns The user's email if found, undefined otherwise
  */
-export function getUserEmail(userId: number): string {
+export function getUserEmail(userId: number): string | undefined {
   const user = getUserById(userId);
-  // This will throw TypeError if user doesn't exist
-  return user.email;
+  return user?.email;
 }
 
 /**
  * Check if user is admin
- * BUG: No null check before accessing role property
+ * @param userId - The user ID to check
+ * @returns True if user exists and is admin, false otherwise
  */
 export function isAdmin(userId: number): boolean {
   const user = getUserById(userId);
-  // Another potential TypeError here
-  return user.role === 'admin';
+  return user?.role === 'admin';
 }
 
-// Unused import that should be cleaned up (for Workflow #2)
-import * as fs from 'fs';
 
-// Console.log that should be removed (for Workflow #2)
-console.log('Users API loaded');
 
 /**
  * Format user display name
- * Missing proper formatting and has inconsistent spacing
+ * @param user - The user object
+ * @returns The formatted display name in uppercase
  */
 export function formatUserName(user: User): string {
-    // Inconsistent indentation (for ESLint to catch)
-    const displayName=user.name.toUpperCase();  // Missing spaces around =
-  return displayName
-  // Missing semicolon above (for Prettier to fix)
+  const displayName = user.name.toUpperCase();
+  return displayName;
 }
\ No newline at end of file