Add project files.

test/integration/Elsa.Workflows.IntegrationTests/Scenarios/SetGetVariablesFromActivities/Activities/CreateVariableActivity.cs

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+using Elsa.Extensions;
+
+namespace Elsa.Workflows.IntegrationTests.Scenarios.SetGetVariablesFromActivities.Activities;
+
+public class CreateVariableActivity : CodeActivity
+{
+    protected override void Execute(ActivityExecutionContext context)
+    {
+        context.SetVariable("Foo", "Bar");
+    }
+}

test/integration/Elsa.Workflows.IntegrationTests/Scenarios/SetGetVariablesFromActivities/Activities/ReadVariableActivity.cs

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+using Elsa.Extensions;
+
+namespace Elsa.Workflows.IntegrationTests.Scenarios.SetGetVariablesFromActivities.Activities;
+
+public class ReadVariableActivity : CodeActivity<string>
+{
+    protected override void Execute(ActivityExecutionContext context)
+    {
+        var foo = context.GetVariable<string>("Foo");
+        Result.Set(context, foo);
+    }
+}

test/integration/Elsa.Workflows.IntegrationTests/Scenarios/SetGetVariablesFromActivities/Tests.cs

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+using Elsa.Testing.Shared;
+using Elsa.Workflows.IntegrationTests.Scenarios.SetGetVariablesFromActivities.Workflows;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit.Abstractions;
+
+namespace Elsa.Workflows.IntegrationTests.Scenarios.SetGetVariablesFromActivities;
+
+public class Tests
+{
+    private readonly IWorkflowRunner _workflowRunner;
+    private readonly CapturingTextWriter _capturingTextWriter = new();
+    private readonly IServiceProvider _services;
+
+    public Tests(ITestOutputHelper testOutputHelper)
+    {
+        _services = new TestApplicationBuilder(testOutputHelper).WithCapturingTextWriter(_capturingTextWriter).Build();
+        _services.GetRequiredService<IWorkflowBuilderFactory>();
+        _workflowRunner = _services.GetRequiredService<IWorkflowRunner>();
+    }
+
+    [Fact(DisplayName = "Activities can set and get variables internally")]
+    public async Task Test1()
+    {
+        await _services.PopulateRegistriesAsync(); 
+        await _workflowRunner.RunAsync<SampleWorkflow>();
+        var lines = _capturingTextWriter.Lines.ToList();
+        Assert.Equal(new[] { "Bar" }, lines);
+    }
+}

test/integration/Elsa.Workflows.IntegrationTests/Scenarios/SetGetVariablesFromActivities/Workflows/SampleWorkflow.cs

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+using Elsa.Workflows.Activities;
+using Elsa.Workflows.IntegrationTests.Scenarios.SetGetVariablesFromActivities.Activities;
+using Elsa.Workflows.Memory;
+
+namespace Elsa.Workflows.IntegrationTests.Scenarios.SetGetVariablesFromActivities.Workflows;
+
+class SampleWorkflow : WorkflowBase
+{
+    protected override void Build(IWorkflowBuilder workflow)
+    {
+        var variable1 = new Variable<string>("Variable1", "");
+
+        workflow.Root = new Sequence
+        {
+            Variables =
+            {
+                variable1
+            },
+
+            Activities =
+            {
+                new CreateVariableActivity(),
+                new ReadVariableActivity
+                {
+                    Result = new(variable1)
+                },
+                new WriteLine(variable1)
+            }
+        };
+    }
+}