diff --git a/tests/Application.UnitTest/Common/Results/ResultTests.cs b/tests/Application.UnitTest/Common/Results/ResultTests.cs
new file mode 100644
index 0000000..ece8bec
--- /dev/null
+++ b/tests/Application.UnitTest/Common/Results/ResultTests.cs
@@ -0,0 +1,64 @@
+using Application.Common.Results;
+
+namespace Application.UnitTest.Common.Results;
+
+public class ResultTests
+{
+    [Fact]
+    public void Success_ShouldReturnResultWithIsSuccessTrue()
+    {
+        var result = Result.Success();
+        Assert.True(result.IsSuccess);
+        Assert.False(result.IsFailure);
+        Assert.Equal(ErrorTypeConstant.None, result.Error.Code);
+    }
+
+    [Fact]
+    public void Success_WithValue_ShouldReturnResultWithValue()
+    {
+        var result = Result.Success("test-value");
+        Assert.True(result.IsSuccess);
+        Assert.Equal("test-value", result.Value);
+    }
+
+    [Fact]
+    public void Failure_ShouldReturnResultWithIsFailureTrue()
+    {
+        var error = new Error("TestError", "Something went wrong");
+        var result = Result.Failure(error);
+        Assert.True(result.IsFailure);
+        Assert.False(result.IsSuccess);
+        Assert.Equal("TestError", result.Error.Code);
+        Assert.Equal("Something went wrong", result.Error.Message);
+    }
+
+    [Fact]
+    public void Failure_WithValueType_ShouldReturnTypedResult()
+    {
+        var error = new Error("NotFound", "Item not found");
+        var result = Result.Failure<string>(error);
+        Assert.True(result.IsFailure);
+        Assert.Throws<InvalidOperationException>(() => result.Value);
+    }
+
+    [Fact]
+    public void Constructor_ShouldThrow_WhenSuccessWithError()
+    {
+        var error = new Error("SomeError", "message");
+        Assert.Throws<InvalidOperationException>(() => new ResultTestCase(true, error));
+    }
+
+    [Fact]
+    public void Constructor_ShouldThrow_WhenFailureWithNoError()
+    {
+        var noneError = new Error("None", string.Empty);
+        Assert.Throws<InvalidOperationException>(() => new ResultTestCase(false, noneError));
+    }
+}
+
+public class ResultTestCase : Result
+{
+    public ResultTestCase(bool isSuccess, Error error) : base(isSuccess, error)
+    {
+    }
+}
diff --git a/tests/Application.UnitTest/DTOs/PagedResultTests.cs b/tests/Application.UnitTest/DTOs/PagedResultTests.cs
new file mode 100644
index 0000000..21bd50d
--- /dev/null
+++ b/tests/Application.UnitTest/DTOs/PagedResultTests.cs
@@ -0,0 +1,110 @@
+using Application.DTOs;
+
+namespace Application.UnitTest.DTOs;
+
+public class PagedResultTests
+{
+    [Fact]
+    public void TotalPages_ShouldCalculateCorrectly_WhenExactDivision()
+    {
+        var paged = new PagedResult<string>
+        {
+            Items = ["a", "b", "c", "d", "e"],
+            TotalCount = 5,
+            PageNumber = 1,
+            PageSize = 5
+        };
+        Assert.Equal(1, paged.TotalPages);
+    }
+
+    [Fact]
+    public void TotalPages_ShouldRoundUp_WhenNotExactDivision()
+    {
+        var paged = new PagedResult<string>
+        {
+            Items = ["a", "b", "c"],
+            TotalCount = 10,
+            PageNumber = 1,
+            PageSize = 3
+        };
+        Assert.Equal(4, paged.TotalPages);
+    }
+
+    [Fact]
+    public void TotalPages_ShouldBeZero_WhenTotalCountIsZero()
+    {
+        var paged = new PagedResult<string>
+        {
+            Items = [],
+            TotalCount = 0,
+            PageNumber = 1,
+            PageSize = 10
+        };
+        Assert.Equal(0, paged.TotalPages);
+    }
+
+    [Fact]
+    public void HasPreviousPage_ShouldBeFalse_WhenOnFirstPage()
+    {
+        var paged = new PagedResult<string>
+        {
+            Items = [],
+            TotalCount = 20,
+            PageNumber = 1,
+            PageSize = 10
+        };
+        Assert.False(paged.HasPreviousPage);
+    }
+
+    [Fact]
+    public void HasPreviousPage_ShouldBeTrue_WhenPastFirstPage()
+    {
+        var paged = new PagedResult<string>
+        {
+            Items = [],
+            TotalCount = 20,
+            PageNumber = 2,
+            PageSize = 10
+        };
+        Assert.True(paged.HasPreviousPage);
+    }
+
+    [Fact]
+    public void HasNext_ShouldBeFalse_WhenOnLastPage()
+    {
+        var paged = new PagedResult<string>
+        {
+            Items = [],
+            TotalCount = 20,
+            PageNumber = 2,
+            PageSize = 10
+        };
+        Assert.False(paged.HasNext);
+    }
+
+    [Fact]
+    public void HasNext_ShouldBeTrue_WhenMorePagesExist()
+    {
+        var paged = new PagedResult<string>
+        {
+            Items = [],
+            TotalCount = 20,
+            PageNumber = 1,
+            PageSize = 10
+        };
+        Assert.True(paged.HasNext);
+    }
+
+    [Fact]
+    public void HasNext_ShouldBeFalse_WhenOnlyOnePage()
+    {
+        var paged = new PagedResult<string>
+        {
+            Items = [],
+            TotalCount = 3,
+            PageNumber = 1,
+            PageSize = 10
+        };
+        Assert.False(paged.HasNext);
+    }
+}
diff --git a/tests/Application.UnitTest/Services/AuthenticationServiceTests.cs b/tests/Application.UnitTest/Services/AuthenticationServiceTests.cs
index 7bd5a95..c39e31e 100644
--- a/tests/Application.UnitTest/Services/AuthenticationServiceTests.cs
+++ b/tests/Application.UnitTest/Services/AuthenticationServiceTests.cs
@@ -134,6 +134,28 @@ public class AuthenticationServiceTests
         Assert.Equal(AuthError.UserNotFound, result.Error);
     }
 
+    [Fact]
+    public async Task LoginAsync_ShouldReturnFailure_WhenPasswordIsWrong()
+    {
+        var password = "ValidP@ss1!";
+        var user = new User
+        {
+            Id = 1,
+            Username = "testuser",
+            Email = "test@example.com",
+            Password = new PasswordHasher<User>().HashPassword(
+                new User { Username = "testuser", Email = "test@example.com", Password = password },
+                password)
+        };
+        var request = new LoginRequest(user.Email, "WrongPassword1!");
+        _userRepository.GetUserByEmailAsync(request.Email).Returns(user);
+
+        var result = await _sut.LoginAsync(request);
+
+        Assert.True(result.IsFailure);
+        Assert.Equal(AuthError.InvalidPassword, result.Error);
+    }
+
     [Fact]
     public async Task RefreshTokensAsync_ShouldReturnSuccess_WhenRefreshTokenIsValid()
     {
diff --git a/tests/Application.UnitTest/Services/EmailServiceTests.cs b/tests/Application.UnitTest/Services/EmailServiceTests.cs
new file mode 100644
index 0000000..2977357
--- /dev/null
+++ b/tests/Application.UnitTest/Services/EmailServiceTests.cs
@@ -0,0 +1,60 @@
+using Application.Models;
+using Application.Services;
+using MailKit.Net.Smtp;
+using Microsoft.Extensions.Configuration;
+using MimeKit;
+using NSubstitute;
+
+namespace Application.UnitTest.Services;
+
+public class EmailServiceTests
+{
+    private readonly IConfiguration _configuration = Substitute.For<IConfiguration>();
+    private readonly ISmtpClient _smtpClient = Substitute.For<ISmtpClient>();
+    private readonly EmailService _sut;
+
+    public EmailServiceTests()
+    {
+        _configuration["EmailSettings:From"].Returns("sender@gmail.com");
+        _configuration["EmailSettings:SmtpServer"].Returns("smtp.gmail.com");
+        _configuration["EmailSettings:Password"].Returns("app-password");
+
+        _sut = new EmailService(_configuration, () => _smtpClient);
+    }
+
+    [Fact]
+    public void SendEmailAsync_ShouldConnectAndAuthenticate()
+    {
+        var request = new EmailRequest("recipient@example.com", "Test Subject", "<p>Hello</p>");
+
+        _sut.SendEmailAsync(request);
+
+        _smtpClient.Received(1).Connect("smtp.gmail.com", 465, true);
+        _smtpClient.Received(1).Authenticate("sender@gmail.com", "app-password");
+        _smtpClient.Received(1).Send(Arg.Any<MimeMessage>());
+        _smtpClient.Received(1).Disconnect(true);
+    }
+
+    [Fact]
+    public void SendEmailAsync_ShouldSendMessageWithCorrectDetails()
+    {
+        var request = new EmailRequest("recipient@example.com", "Welcome!", "<h1>Hi</h1>");
+
+        _sut.SendEmailAsync(request);
+
+        _smtpClient.Received(1).Send(Arg.Is<MimeMessage>(msg =>
+            msg.To.Mailboxes.Any(m => m.Address == "recipient@example.com") &&
+            msg.Subject == "Welcome!"));
+    }
+
+    [Fact]
+    public void SendEmailAsync_ShouldDisposeClient_AfterSending()
+    {
+        var request = new EmailRequest("recipient@example.com", "Subject", "Body");
+
+        _sut.SendEmailAsync(request);
+
+        _smtpClient.Received(1).Disconnect(true);
+        _smtpClient.Received(1).Dispose();
+    }
+}
diff --git a/tests/Application.UnitTest/Services/JwtServiceTests.cs b/tests/Application.UnitTest/Services/JwtServiceTests.cs
new file mode 100644
index 0000000..bf98d55
--- /dev/null
+++ b/tests/Application.UnitTest/Services/JwtServiceTests.cs
@@ -0,0 +1,170 @@
+using System.IdentityModel.Tokens.Jwt;
+using Application.Services;
+using Domain.Entities;
+using Domain.Interface;
+using Microsoft.Extensions.Configuration;
+using NSubstitute;
+
+namespace Application.UnitTest.Services;
+
+public class JwtServiceTests
+{
+    private readonly IConfiguration _configuration = Substitute.For<IConfiguration>();
+    private readonly IUserRepository _userRepository = Substitute.For<IUserRepository>();
+    private readonly IUnitOfWork _unitOfWork = Substitute.For<IUnitOfWork>();
+    private readonly JwtService _sut;
+
+    public JwtServiceTests()
+    {
+        var section = Substitute.For<IConfigurationSection>();
+        section.Value.Returns("veryveryveryveryveryveryverysecretkey");
+        _configuration.GetSection("Jwt:Key").Returns(section);
+
+        _configuration["Jwt:Key"].Returns("veryveryveryveryveryveryverysecretkey");
+        _configuration["Jwt:Issuer"].Returns("https://localhost:7091");
+        _configuration["Jwt:Audience"].Returns("http://localhost:5184");
+
+        _sut = new JwtService(_configuration, _userRepository, _unitOfWork);
+    }
+
+    [Fact]
+    public async Task GenerateTokenAsync_ShouldReturnToken_WhenUserIsValid()
+    {
+        var user = new User
+        {
+            Id = 1,
+            Username = "testuser",
+            Email = "test@example.com",
+            Password = "hash"
+        };
+        _userRepository.GetUserRolesByEmailAsync(user.Email)
+            .Returns(["User"]);
+
+        var token = await _sut.GenerateTokenAsync(user);
+
+        Assert.NotNull(token);
+        Assert.NotEmpty(token);
+
+        var handler = new JwtSecurityTokenHandler();
+        var jwtToken = handler.ReadJwtToken(token);
+
+        Assert.Equal("https://localhost:7091", jwtToken.Issuer);
+        Assert.Contains(jwtToken.Claims, c => c.Type == "email" && c.Value == user.Email);
+        Assert.Contains(jwtToken.Claims, c => c.Type == "UserId" && c.Value == "1");
+        Assert.Contains(jwtToken.Claims, c => c.Type == "username" && c.Value == user.Username);
+        Assert.Contains(jwtToken.Claims, c => c.Type == "role" && c.Value == "User");
+    }
+
+    [Fact]
+    public async Task GenerateTokenAsync_ShouldIncludeAllRoles()
+    {
+        var user = new User
+        {
+            Id = 2,
+            Username = "adminuser",
+            Email = "admin@example.com",
+            Password = "hash"
+        };
+        _userRepository.GetUserRolesByEmailAsync(user.Email)
+            .Returns(["Admin", "User"]);
+
+        var token = await _sut.GenerateTokenAsync(user);
+
+        var handler = new JwtSecurityTokenHandler();
+        var jwtToken = handler.ReadJwtToken(token);
+        var roleClaims = jwtToken.Claims.Where(c => c.Type == "role").Select(c => c.Value).ToList();
+
+        Assert.Contains("Admin", roleClaims);
+        Assert.Contains("User", roleClaims);
+    }
+
+    [Fact]
+    public async Task GenerateAndSaveRefreshTokenAsync_ShouldUpdateUserAndCommit()
+    {
+        var user = new User
+        {
+            Id = 1,
+            Username = "testuser",
+            Email = "test@example.com",
+            Password = "hash"
+        };
+
+        var refreshToken = await _sut.GenerateAndSaveRefreshTokenAsync(user);
+
+        Assert.NotNull(refreshToken);
+        Assert.NotEmpty(refreshToken);
+        Assert.Equal(refreshToken, user.RefreshToken);
+        Assert.NotNull(user.RefreshTokenExpiryTime);
+        Assert.True(user.RefreshTokenExpiryTime > DateTime.UtcNow);
+        _userRepository.Received(1).Update(user);
+        await _unitOfWork.Received(1).CommitAsync();
+    }
+
+    [Fact]
+    public async Task ValidateRefreshTokenAsync_ShouldReturnNull_WhenUserNotFound()
+    {
+        _userRepository.GetUserByIdAsync(99).Returns((User?)null);
+
+        var result = await _sut.ValidateRefreshTokenAsync(99, "some-token");
+
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public async Task ValidateRefreshTokenAsync_ShouldReturnNull_WhenTokenMismatch()
+    {
+        var user = new User
+        {
+            Id = 1,
+            Username = "testuser",
+            Email = "test@example.com",
+            Password = "hash",
+            RefreshToken = "stored-token",
+            RefreshTokenExpiryTime = DateTime.UtcNow.AddDays(1)
+        };
+        _userRepository.GetUserByIdAsync(1).Returns(user);
+
+        var result = await _sut.ValidateRefreshTokenAsync(1, "wrong-token");
+
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public async Task ValidateRefreshTokenAsync_ShouldReturnNull_WhenTokenExpired()
+    {
+        var user = new User
+        {
+            Id = 1,
+            Username = "testuser",
+            Email = "test@example.com",
+            Password = "hash",
+            RefreshToken = "expired-token",
+            RefreshTokenExpiryTime = DateTime.UtcNow.AddDays(-1)
+        };
+        _userRepository.GetUserByIdAsync(1).Returns(user);
+
+        var result = await _sut.ValidateRefreshTokenAsync(1, "expired-token");
+
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public async Task ValidateRefreshTokenAsync_ShouldReturnUser_WhenTokenValid()
+    {
+        var user = new User
+        {
+            Id = 1,
+            Username = "testuser",
+            Email = "test@example.com",
+            Password = "hash",
+            RefreshToken = "valid-token",
+            RefreshTokenExpiryTime = DateTime.UtcNow.AddDays(1)
+        };
+        _userRepository.GetUserByIdAsync(1).Returns(user);
+
+        var result = await _sut.ValidateRefreshTokenAsync(1, "valid-token");
+
+        Assert.NotNull(result);
+        Assert.Equal(1, result.Id);
+    }
+}