* Added missing files

HeartBeatServer.Tests/Core/AppTests.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Threading.Tasks;
+using Moq;
+using Xunit;
+using HeartBeatServers.Core;
+using Services.Vault;
+
+namespace HeartBeatServers.Core
+{
+    public class AppTests
+    {
+        [Fact]
+        public async Task RunAsync_ShouldInsertHeartBeat_WhenNoPreviousResult()
+        {
+            // Arrange
+            var vaultService = new Mock<IVaultService>();
+            var app = new App(null, vaultService.Object);
+
+            // TODO: Mock vaultService.GetSecretAsync to return connection string
+            // TODO: Mock GetLastUpdateDate to return null via partial or extracting method for test
+            // TODO: Mock InsertHeartBeat to track invocation
+
+            // Act
+            await app.RunAsync();
+
+            // Assert
+            // TODO: Verify InsertHeartBeat was called
+        }
+
+        [Fact]
+        public async Task RunAsync_ShouldUpdateHeartBeat_WhenPreviousResultExists()
+        {
+            // Arrange
+            var vaultService = new Mock<IVaultService>();
+            var app = new App(null, vaultService.Object);
+
+            // TODO: Mock vaultService.GetSecretAsync to return connection string
+            // TODO: Mock GetLastUpdateDate to return a valid ResultModel
+            // TODO: Mock UpdateHeartBeat to track invocation
+
+            // Act
+            await app.RunAsync();
+
+            // Assert
+            // TODO: Verify UpdateHeartBeat was called
+        }
+
+        // Additional tests can be added for private methods via reflection or refactoring
+    }
+}

HeartBeatServer.Tests/Services/IEmailGeneratorServiceTests.cs

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+using System;
+using Xunit;
+using HeartBeatServers.Services;
+using Moq;
+using HeartBeatServers.Models;
+
+namespace HeartBeatServers.Services
+{
+    public class IEmailGeneratorServiceTests
+    {
+        [Fact]
+        public void SendEmail_InterfaceMethod_CallMock()
+        {
+            // Arrange
+            var mockService = new Mock<IEmailGeneratorService>();
+            var email = new EmailModel();
+
+            // Act
+            mockService.Object.SendEmail(email);
+
+            // Assert
+            mockService.Verify(s => s.SendEmail(email), Times.Once);
+        }
+    }
+}