Add unit tests for FlowFork activity and enhance test utilities (#6995)

* Add unit tests for `FlowFork` activity and enhance test utilities

- Introduce `FlowForkTests` to validate activity behavior with various branch configurations.
- Extend `ActivityExecutionContextExtensions` with methods to retrieve and check outcomes.
- Modify `ActivityTestFixture` to ensure activities transition to `Running` status before execution.

* Apply suggestion from @Copilot

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/ActivityExecutionContextExtensions.cs

@@ -17,4 +17,16 @@ public static class ActivityExecutionContextExtensions
     {
         return activityExecutionContext.WorkflowExecutionContext.Scheduler.Find(x => x.Activity == activity) != null;
     }
+    
+    public static IEnumerable<string> GetOutcomes(this ActivityExecutionContext activityExecutionContext)
+    {
+        if (activityExecutionContext.JournalData.TryGetValue("Outcomes", out var outcomesObj) && outcomesObj is string[] outcomes)
+            return outcomes;
+        return [];
+    }
+    
+    public static bool HasOutcome(this ActivityExecutionContext activityExecutionContext, string outcome)
+    {
+        return activityExecutionContext.GetOutcomes().Contains(outcome);
+    }
 }

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

@@ -83,6 +83,7 @@ public class ActivityTestFixture
         // Set up variables and inputs, then execute the activity
         await SetupExistingVariablesAsync(Activity, context);
         await context.EvaluateInputPropertiesAsync();
+        context.TransitionTo(ActivityStatus.Running);
         await Activity.ExecuteAsync(context);
 
         return context;

test/unit/Elsa.Activities.UnitTests/Branching/FlowForkTests.cs

@@ -0,0 +1,40 @@
+using Elsa.Testing.Shared;
+using Elsa.Workflows;
+using Elsa.Workflows.Activities.Flowchart.Activities;
+
+namespace Elsa.Activities.UnitTests.Branching;
+
+public class FlowForkTests
+{
+    [Theory]
+    [MemberData(nameof(BranchTestCases))]
+    public async Task Should_Complete_With_Specified_Branches(string[] branches, string[] expectedOutcomes)
+    {
+        // Arrange
+        var flowFork = new FlowFork();
+        if (branches.Length > 0)
+            flowFork.Branches = new(branches);
+
+        // Act
+        var context = await ExecuteAsync(flowFork);
+
+        // Assert - Activity should complete with all outcomes.
+        var outcomes = context.GetOutcomes().ToList();
+
+        Assert.Equal(expectedOutcomes.Length, outcomes.Count);
+        foreach (var expectedOutcome in expectedOutcomes)
+            Assert.Contains(expectedOutcome, outcomes);
+    }
+
+    public static IEnumerable<object[]> BranchTestCases()
+    {
+        yield return [Array.Empty<string>(), new[] { "Done" }];
+        yield return [new[] { "SingleBranch" }, new[] { "SingleBranch" }];
+        yield return [new[] { "Branch1", "Branch2", "Branch3" }, new[] { "Branch1", "Branch2", "Branch3" }];
+    }
+
+    private static Task<ActivityExecutionContext> ExecuteAsync(IActivity activity)
+    {
+        return new ActivityTestFixture(activity).ExecuteAsync();
+    }
+}