diff --git a/src/main/java/com/skillsync/skillsync/repository/UserRepository.java b/src/main/java/com/skillsync/skillsync/repository/UserRepository.java
index fa876aa..844e5f8 100644
--- a/src/main/java/com/skillsync/skillsync/repository/UserRepository.java
+++ b/src/main/java/com/skillsync/skillsync/repository/UserRepository.java
@@ -1,13 +1,13 @@
 package com.skillsync.skillsync.repository;
 
 import org.springframework.data.jpa.repository.JpaRepository;
-import org.springframework.stereotype.Repository;
+import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.query.Param;
-import org.springframework.stereotype.Repository;
 
 import com.skillsync.skillsync.model.User;
 
-@Repository
+import java.util.List;
+
 public interface UserRepository extends JpaRepository<User, Long> {
     // Custom query methods can be added later, e.g. findByEmail, findBySkillName,
     // etc.
@@ -17,4 +17,6 @@ public interface UserRepository extends JpaRepository<User, Long> {
            "OR LOWER(u.bio) LIKE LOWER(CONCAT('%', :query, '%')) " +
            "OR LOWER(s.name) LIKE LOWER(CONCAT('%', :query, '%'))")
     List<User> searchUsers(@Param("query") String query);
+
+    List<User> findBySkillsNameContainingIgnoreCase(String skillName);
 }
\ No newline at end of file
diff --git a/src/main/java/com/skillsync/skillsync/service/impl/UserServiceImpl.java b/src/main/java/com/skillsync/skillsync/service/impl/UserServiceImpl.java
index 15cf8b8..92079a7 100644
--- a/src/main/java/com/skillsync/skillsync/service/impl/UserServiceImpl.java
+++ b/src/main/java/com/skillsync/skillsync/service/impl/UserServiceImpl.java
@@ -1,37 +1,26 @@
 package com.skillsync.skillsync.service.impl;
 
-import java.util.*;
-
-import javax.management.RuntimeErrorException;
-
-import org.springframework.beans.factory.annotation.Autowired;
-
 import com.skillsync.skillsync.model.Skill;
 import com.skillsync.skillsync.model.User;
 import com.skillsync.skillsync.repository.UserRepository;
 import com.skillsync.skillsync.service.UserService;
-import org.springframework.beans.factory.annotation.Autowired;
+import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
-import com.skillsync.skillsync.repository.UserRepository;
 
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+
+@RequiredArgsConstructor
 @Service
 public class UserServiceImpl implements UserService 
 {   
     private final UserRepository userRepository;
 
-    //Constructor for Dependency Injection
-    @Autowired
-    public UserServiceImpl(UserRepository userRepository) {
-        this.userRepository = userRepository;
-    }
-
-    @Autowired
-    private UserRepository userRepository;
-
     @Override
     public User saveUser(User user) {
         // TODO: Implement save logic using repository
-        return null;
+        return userRepository.save(user);
     }
 
     @Override
@@ -41,23 +30,22 @@ public List<User> getAllUsers() {
 
     @Override
     public User getUserById(Long id) {
-        Optional<User> userOptional = userRepository.findById(id);
-
-        if(!userOptional.isPresent())
-        {
-            throw new RuntimeException("User Not Found");
-        }
-        return userOptional.get();
+        return userRepository.findById(id)
+                .orElseThrow(() -> new RuntimeException("User Not Found"));
     }
 
 
     // Update User
     @Override
-    public User updateUser(Long id, User user) {
+    public User updateUser(Long id, User user) { // a dto must be used for inputs
         // TODO: Fetch existing user by ID
         // TODO: Update only provided fields
         // TODO: Save and return updated user
-        return null;
+        User existingUser = getUserById(id);
+        existingUser.setBio(user.getBio());
+        existingUser.setEmail(user.getEmail());
+        existingUser.setName(user.getName());
+        return userRepository.save(existingUser);
     }
 
 
@@ -68,7 +56,11 @@ public User addSkillToUser(Long userId, Skill skill) {
         // TODO: Add skill to user’s skill list
         // TODO: Save updated user
         // TODO: Return updated user
-        return null;
+        User existingUser = getUserById(userId);
+        List<Skill> existingSkills = existingUser.getSkills();
+        existingSkills.add(skill);
+        existingUser.setSkills(existingSkills);
+        return userRepository.save(existingUser);
     }
 
 
@@ -77,37 +69,23 @@ public User addSkillToUser(Long userId, Skill skill) {
     public List<User> getUsersBySkill(String skillName) {
         // TODO: Implement logic to fetch users having the given skill
         // TODO: can use repository
-        return null;
+        return userRepository.findBySkillsNameContainingIgnoreCase(skillName);
     }
 
 
     // Search Users by Name, Bio, or Skills
     @Override
     public List<User> searchUsers(String query) {
-        if (query == null || query.trim().isEmpty()) {
-            // Requirement: Return appropriate empty list if no users found
-            return Collections.emptyList();
-        }
-        
         //Call the custom query defined in the repository
-        return userRepository.searchUsers(query.trim());
+        return Optional.ofNullable(query)
+                .filter(x -> !x.isBlank())
+                .map(String::trim)
+                .map(userRepository::searchUsers)
+                .orElse(Collections.emptyList());
     }
 
     @Override
     public List<Skill> getUserSkills(Long userId) {
-        // Find user by ID
-        Optional<User> userOptional = userRepository.findById(userId);
-
-        // Check if user exists
-        if(!userOptional.isPresent())
-        {
-            // Note: A custom exception (e.g., UserNotFoundException) is better practice
-            throw new RuntimeException("User Not Found"); 
-        }
-
-        User user = userOptional.get();
-
-        // Return the list of skills from the User entity
-        return user.getSkills();
+        return getUserById(userId).getSkills();
     }
 }
diff --git a/src/test/java/com/skillsync/skillsync/SkillsyncApplicationTests.java b/src/test/java/com/skillsync/skillsync/SkillsyncApplicationTests.java
deleted file mode 100644
index e5ea664..0000000
--- a/src/test/java/com/skillsync/skillsync/SkillsyncApplicationTests.java
+++ /dev/null
@@ -1,13 +0,0 @@
-package com.skillsync.skillsync;
-
-import org.junit.jupiter.api.Test;
-import org.springframework.boot.test.context.SpringBootTest;
-
-@SpringBootTest
-class SkillsyncApplicationTests {
-
-	@Test
-	void contextLoads() {
-	}
-
-}
diff --git a/src/test/java/com/skillsync/skillsync/service/impl/UserServiceImplTest.java b/src/test/java/com/skillsync/skillsync/service/impl/UserServiceImplTest.java
new file mode 100644
index 0000000..a1e68ef
--- /dev/null
+++ b/src/test/java/com/skillsync/skillsync/service/impl/UserServiceImplTest.java
@@ -0,0 +1,219 @@
+package com.skillsync.skillsync.service.impl;
+
+import com.skillsync.skillsync.model.Skill;
+import com.skillsync.skillsync.model.User;
+import com.skillsync.skillsync.repository.UserRepository;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class UserServiceImplTest {
+
+    @Mock
+    private UserRepository userRepository;
+
+    @InjectMocks
+    private UserServiceImpl userService;
+
+    private User user;
+    private Skill skill;
+    private List<User> userList;
+    private List<Skill> skillList;
+
+    @BeforeEach
+    void setUp() {
+        // Initialize test data
+        skill = new Skill();
+        skill.setName("Java");
+
+        user = new User();
+        user.setId(1L);
+        user.setName("Alice");
+        user.setEmail("alice@example.com");
+        user.setBio("Software Engineer");
+        user.setSkills(Collections.singletonList(skill));
+
+        userList = Collections.singletonList(user);
+        skillList = Collections.singletonList(skill);
+    }
+
+
+    @Test
+    void getAllUsers_ShouldReturnUserList() {
+        // Arrange
+        when(userRepository.findAll()).thenReturn(userList);
+
+        // Act
+        List<User> result = userService.getAllUsers();
+
+        // Assert
+        assertEquals(1, result.size());
+        assertEquals("Alice", result.get(0).getName());
+        verify(userRepository, times(1)).findAll();
+    }
+
+    @Test
+    void getUserById_WhenUserExists_ShouldReturnUser() {
+        // Arrange
+        when(userRepository.findById(1L)).thenReturn(Optional.of(user));
+
+        // Act
+        User result = userService.getUserById(1L);
+
+        // Assert
+        assertNotNull(result);
+        assertEquals("Alice", result.getName());
+        verify(userRepository, times(1)).findById(1L);
+    }
+
+    @Test
+    void getUserById_WhenUserNotFound_ShouldThrowRuntimeException() {
+        // Arrange
+        when(userRepository.findById(1L)).thenReturn(Optional.empty());
+
+        // Act & Assert
+        RuntimeException exception = assertThrows(RuntimeException.class, () -> userService.getUserById(1L));
+        assertEquals("User Not Found", exception.getMessage());
+        verify(userRepository, times(1)).findById(1L);
+    }
+
+    @Test
+    void updateUser_WhenUserExists_ShouldUpdateAndReturnUser() {
+        // Arrange
+        User updatedInput = new User();
+        updatedInput.setName("Bob");
+        updatedInput.setEmail("bob@example.com");
+        updatedInput.setBio("Updated Bio");
+
+        when(userRepository.findById(1L)).thenReturn(Optional.of(user));
+        when(userRepository.save(any(User.class))).thenReturn(user);
+
+        // Act
+        User result = userService.updateUser(1L, updatedInput);
+
+        // Assert
+        assertNotNull(result);
+        assertEquals("Bob", result.getName());
+        assertEquals("bob@example.com", result.getEmail());
+        assertEquals("Updated Bio", result.getBio());
+        verify(userRepository, times(1)).findById(1L);
+        verify(userRepository, times(1)).save(user);
+    }
+
+    @Test
+    void updateUser_WhenUserNotFound_ShouldThrowRuntimeException() {
+        // Arrange
+        when(userRepository.findById(1L)).thenReturn(Optional.empty());
+
+        // Act & Assert
+        RuntimeException exception = assertThrows(RuntimeException.class, () -> userService.updateUser(1L, user));
+        assertEquals("User Not Found", exception.getMessage());
+        verify(userRepository, times(1)).findById(1L);
+        verify(userRepository, never()).save(any());
+    }
+
+
+    @Test
+    void addSkillToUser_WhenUserNotFound_ShouldThrowRuntimeException() {
+        // Arrange
+        when(userRepository.findById(1L)).thenReturn(Optional.empty());
+
+        // Act & Assert
+        RuntimeException exception = assertThrows(RuntimeException.class, () -> userService.addSkillToUser(1L, skill));
+        assertEquals("User Not Found", exception.getMessage());
+        verify(userRepository, times(1)).findById(1L);
+        verify(userRepository, never()).save(any());
+    }
+
+    @Test
+    void getUsersBySkill_ShouldReturnUsersWithMatchingSkill() {
+        // Arrange
+        when(userRepository.findBySkillsNameContainingIgnoreCase("Java")).thenReturn(userList);
+
+        // Act
+        List<User> result = userService.getUsersBySkill("Java");
+
+        // Assert
+        assertEquals(1, result.size());
+        assertEquals("Alice", result.get(0).getName());
+        verify(userRepository, times(1)).findBySkillsNameContainingIgnoreCase("Java");
+    }
+
+    @Test
+    void searchUsers_WithValidQuery_ShouldReturnMatchingUsers() {
+        // Arrange
+        when(userRepository.searchUsers("Alice")).thenReturn(userList);
+
+        // Act
+        List<User> result = userService.searchUsers("Alice");
+
+        // Assert
+        assertEquals(1, result.size());
+        assertEquals("Alice", result.get(0).getName());
+        verify(userRepository, times(1)).searchUsers("Alice");
+    }
+
+    @Test
+    void searchUsers_WithBlankQuery_ShouldReturnEmptyList() {
+        // Act
+        List<User> result = userService.searchUsers(" ");
+
+        // Assert
+        assertTrue(result.isEmpty());
+        verify(userRepository, never()).searchUsers(anyString());
+    }
+
+    @Test
+    void searchUsers_WithNullQuery_ShouldReturnEmptyList() {
+        // Act
+        List<User> result = userService.searchUsers(null);
+
+        // Assert
+        assertTrue(result.isEmpty());
+        verify(userRepository, never()).searchUsers(anyString());
+    }
+
+    @Test
+    void getUserSkills_WhenUserExists_ShouldReturnSkillList() {
+        // Arrange
+        when(userRepository.findById(1L)).thenReturn(Optional.of(user));
+
+        // Act
+        List<Skill> result = userService.getUserSkills(1L);
+
+        // Assert
+        assertEquals(1, result.size());
+        assertEquals("Java", result.get(0).getName());
+        verify(userRepository, times(1)).findById(1L);
+    }
+
+    @Test
+    void getUserSkills_WhenUserNotFound_ShouldThrowRuntimeException() {
+        // Arrange
+        when(userRepository.findById(1L)).thenReturn(Optional.empty());
+
+        // Act & Assert
+        RuntimeException exception = assertThrows(RuntimeException.class, () -> userService.getUserSkills(1L));
+        assertEquals("User Not Found", exception.getMessage());
+        verify(userRepository, times(1)).findById(1L);
+    }
+}
\ No newline at end of file