Enhance MailService: refactor constructor to accept a custom SMTP client factory and add unit tests for SendEmailAsync method

FoodsharingSiegen.Tests/MailServiceTests.cs

@@ -0,0 +1,110 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using FoodsharingSiegen.Contracts.Model;
+using FoodsharingSiegen.Server.Service;
+using MailKit.Net.Smtp;
+using MailKit.Security;
+using Microsoft.Extensions.Options;
+using MimeKit;
+using Moq;
+using Xunit;
+
+namespace FoodsharingSiegen.Tests
+{
+    public class MailServiceTests
+    {
+        private readonly Mock<IOptions<AppSettings>> _mockOptions;
+        private readonly AppSettings _appSettings;
+        private readonly Mock<ISmtpClient> _mockSmtpClient;
+
+        public MailServiceTests()
+        {
+            _appSettings = new AppSettings
+            {
+                Mail = new MailSettings
+                {
+                    Host = "smtp.test.com",
+                    Port = 587,
+                    UseSsl = false,
+                    Username = "user@test.com",
+                    Password = "password123",
+                    FromAddress = "no-reply@test.com"
+                },
+                Terms = new TermSettings
+                {
+                    Title = "Foodsharing Test"
+                }
+            };
+
+            _mockOptions = new Mock<IOptions<AppSettings>>();
+            _mockOptions.Setup(o => o.Value).Returns(_appSettings);
+
+            _mockSmtpClient = new Mock<ISmtpClient>();
+        }
+
+        [Fact]
+        public async Task SendEmailAsync_ConnectsAuthenticatesAndSendsEmail()
+        {
+            // Arrange
+            var service = new MailService(_mockOptions.Object, () => _mockSmtpClient.Object);
+            var toEmail = "recipient@test.com";
+            var subject = "Test Subject";
+            var body = "<p>Test Body</p>";
+
+            // Act
+            await service.SendEmailAsync(toEmail, subject, body);
+
+            // Assert
+            _mockSmtpClient.Verify(
+                x => x.ConnectAsync(
+                    "smtp.test.com", 
+                    587, 
+                    SecureSocketOptions.Auto, 
+                    It.IsAny<CancellationToken>()), 
+                Times.Once);
+
+            _mockSmtpClient.Verify(
+                x => x.AuthenticateAsync(
+                    "user@test.com", 
+                    "password123", 
+                    It.IsAny<CancellationToken>()), 
+                Times.Once);
+
+            // Verify a MimeMessage is passed to SendAsync with correct attributes
+            _mockSmtpClient.Verify(
+                x => x.SendAsync(
+                    It.Is<MimeMessage>(m => m.Subject == subject),
+                    It.IsAny<CancellationToken>(), 
+                    It.IsAny<MailKit.ITransferProgress>()), 
+                Times.Once);
+
+            _mockSmtpClient.Verify(
+                x => x.DisconnectAsync(
+                    true, 
+                    It.IsAny<CancellationToken>()), 
+                Times.Once);
+            
+            _mockSmtpClient.Verify(
+                x => x.Dispose(), 
+                Times.Once);
+        }
+
+        [Fact]
+        public async Task SendEmailAsync_SkipsAuthentication_WhenUsernameIsBlank()
+        {
+            // Arrange
+            _appSettings.Mail.Username = "";
+            _appSettings.Mail.Password = "";
+            var service = new MailService(_mockOptions.Object, () => _mockSmtpClient.Object);
+
+            // Act
+            await service.SendEmailAsync("recipient@test.com", "Subject", "Body");
+
+            // Assert
+            _mockSmtpClient.Verify(
+                x => x.AuthenticateAsync(It.IsAny<string>(), It.IsAny<string>(), It.IsAny<CancellationToken>()), 
+                Times.Never);
+        }
+    }
+}