Add unit tests for Correlate activity and enhance ActivityTestFixture execution functionality (#7119)

* Add unit tests for `Correlate` activity and enhance `ActivityTestFixture` execution functionality

- Introduced `CorrelateTests` to validate correlation ID handling with string literals, inputs, and functions.
- Extended `ActivityTestFixture` with new `ExecuteAsync(ActivityExecutionContext)` overload for improved test execution customization.

* Update src/common/Elsa.Testing.Shared/ActivityTestFixture.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/common/Elsa.Testing.Shared/ActivityTestFixture.cs

@@ -79,7 +79,17 @@ public class ActivityTestFixture
     public async Task<ActivityExecutionContext> ExecuteAsync()
     {
         var context = await BuildAsync();
+        return await ExecuteAsync(context);
+    }
     
+    /// <summary>
+    /// Executes the activity using a pre-built <see cref="ActivityExecutionContext"/>.
+    /// Useful when you need to customize the context before execution, such as setting initial workflow state or overriding correlation IDs.
+    /// </summary>
+    /// <param name="context">The pre-built context to execute</param>
+    /// <returns>The <see cref="ActivityExecutionContext"/> after execution</returns>
+    public async Task<ActivityExecutionContext> ExecuteAsync(ActivityExecutionContext context)
+    {
         // Set up variables and inputs, then execute the activity
         await SetupExistingVariablesAsync(Activity, context);
         await context.EvaluateInputPropertiesAsync();

test/unit/Elsa.Activities.UnitTests/Primitives/CorrelateTests.cs

@@ -0,0 +1,54 @@
+using Elsa.Testing.Shared;
+
+namespace Elsa.Activities.UnitTests.Primitives;
+
+public class CorrelateTests
+{
+    [Fact]
+    public async Task Should_Set_CorrelationId_From_String_Literal()
+    {
+        const string expected = "test-correlation-id";
+        var correlate = new Correlate(expected, null, null);
+
+        await AssertCorrelationIdAsync(correlate, expected);
+    }
+
+    [Fact]
+    public async Task Should_Set_CorrelationId_From_Input()
+    {
+        const string expected = "dynamic-correlation-id";
+        var correlate = new Correlate { CorrelationId = new(expected) };
+
+        await AssertCorrelationIdAsync(correlate, expected);
+    }
+
+    [Fact]
+    public async Task Should_Set_CorrelationId_From_Func()
+    {
+        const string expected = "func-correlation-id";
+        var correlate = new Correlate(_ => expected);
+
+        await AssertCorrelationIdAsync(correlate, expected);
+    }
+
+    [Fact]
+    public async Task Should_Overwrite_Existing_CorrelationId()
+    {
+        const string initial = "initial-correlation-id";
+        const string expected = "updated-correlation-id";
+        var correlate = new Correlate(expected, null, null);
+        var fixture = new ActivityTestFixture(correlate);
+
+        var context = await fixture.BuildAsync();
+        context.WorkflowExecutionContext.CorrelationId = initial;
+        await fixture.ExecuteAsync(context);
+
+        Assert.Equal(expected, context.WorkflowExecutionContext.CorrelationId);
+    }
+
+    private static async Task AssertCorrelationIdAsync(Correlate correlate, string expected)
+    {
+        var context = await new ActivityTestFixture(correlate).ExecuteAsync();
+        Assert.Equal(expected, context.WorkflowExecutionContext.CorrelationId);
+    }
+}