Add integration test for newGuid() in JavaScript evaluator.

Introduces a new unit test in `Elsa.JavaScript.IntegrationTests` to verify that the `newGuid()` function in the JavaScript evaluator correctly returns a `Guid` type.

test/integration/Elsa.JavaScript.IntegrationTests/GuidTests.cs

@@ -0,0 +1,33 @@
+using Elsa.Expressions.Models;
+using Elsa.JavaScript.Contracts;
+using Elsa.Testing.Shared;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit.Abstractions;
+
+namespace Elsa.JavaScript.IntegrationTests;
+
+public class GuidTests
+{
+    private readonly IJavaScriptEvaluator _evaluator;
+    private readonly IServiceProvider _serviceProvider;
+
+    public GuidTests(ITestOutputHelper testOutputHelper)
+    {
+        _serviceProvider = new TestApplicationBuilder(testOutputHelper).Build();
+        _evaluator = _serviceProvider.GetRequiredService<IJavaScriptEvaluator>();
+    }
+    
+    [Fact]
+    public async Task NewGuidReturnsGuid()
+    {
+        //Setup
+        var script = "newGuid()";
+        var expressionExecutionContext = new ExpressionExecutionContext(_serviceProvider, new());
+
+        //Act
+        var result = (Guid)(await _evaluator.EvaluateAsync(script, typeof(Guid), expressionExecutionContext))!;
+
+        //Assert
+        Assert.IsType<Guid>(result);
+    }   
+}