Add unit tests for ReadLine activity (#7110) (#7112)

* Add unit tests for `ReadLine` activity (#7110)

- Implemented `ReadLineTests` to verify the behavior of the `ReadLine` activity.
- Added scenarios for reading input, stream provider usage, and successful completion.
- Refactored `ExecuteAsync` helper to streamline test execution with mock dependencies.

* Enhance `ReadLine` activity tests with additional scenarios: validate null handling, default provider usage, and completion status assertions.

test/unit/Elsa.Activities.UnitTests/Console/ReadLineTests.cs

@@ -0,0 +1,104 @@
+using Elsa.Extensions;
+using Elsa.Testing.Shared;
+using Elsa.Workflows;
+using Microsoft.Extensions.DependencyInjection;
+using NSubstitute;
+
+namespace Elsa.Activities.UnitTests.Console;
+
+/// <summary>
+/// Unit tests for the <see cref="ReadLine"/> activity.
+/// </summary>
+public class ReadLineTests
+{
+    private readonly TextReader _mockTextReader;
+    private readonly IStandardInStreamProvider _mockProvider;
+
+    public ReadLineTests()
+    {
+        _mockTextReader = Substitute.For<TextReader>();
+        _mockProvider = Substitute.For<IStandardInStreamProvider>();
+        _mockProvider.GetTextReader().Returns(_mockTextReader);
+    }
+
+    [Theory(DisplayName = "ReadLine reads text from input and completes successfully")]
+    [InlineData("Hello, World!")]
+    [InlineData("Test input")]
+    [InlineData("")]
+    [InlineData(" ")]
+    [InlineData("\t")]
+    public async Task Should_Read_Text_From_Input_And_Complete(string inputText)
+    {
+        // Arrange
+        var readLine = new ReadLine();
+
+        // Act
+        var context = await ExecuteAsync(readLine, inputText);
+
+        // Assert
+        Assert.Equal(ActivityStatus.Completed, context.Status);
+        var result = (string)context.GetActivityOutput(() => readLine.Result)!;
+        Assert.Equal(inputText, result);
+    }
+
+    [Fact(DisplayName = "ReadLine uses provided stream provider")]
+    public async Task Should_Use_Provided_Stream_Provider()
+    {
+        // Act
+        await ExecuteAsync(new ReadLine());
+
+        // Assert
+        _mockProvider.Received(1).GetTextReader();
+        _mockTextReader.Received(1).ReadLine();
+    }
+
+    [Fact(DisplayName = "ReadLine handles null return value from stream")]
+    public async Task Should_Handle_Null_Return_Value()
+    {
+        // Arrange
+        var readLine = new ReadLine();
+
+        // Act
+        var context = await ExecuteAsync(readLine, null);
+
+        // Assert - The null-forgiving operator in ReadLine implementation means it expects non-null,
+        // but null can occur at end of stream. Verify the behavior stores null.
+        var result = context.GetActivityOutput(() => readLine.Result);
+        Assert.Null(result);
+    }
+
+    [Fact(DisplayName = "ReadLine uses default provider when none is registered")]
+    public async Task Should_Use_Default_Provider_When_None_Registered()
+    {
+        // Arrange
+        var readLine = new ReadLine();
+        const string expectedInput = "Default provider test";
+        var originalConsoleIn = System.Console.In;
+
+        try
+        {
+            // Redirect Console.In to our StringReader
+            System.Console.SetIn(new StringReader(expectedInput));
+
+            // Act
+            var context = await new ActivityTestFixture(readLine).ExecuteAsync();
+
+            // Assert
+            var result = (string)context.GetActivityOutput(() => readLine.Result)!;
+            Assert.Equal(expectedInput, result);
+        }
+        finally
+        {
+            // Restore original Console.In
+            System.Console.SetIn(originalConsoleIn);
+        }
+    }
+
+    private Task<ActivityExecutionContext> ExecuteAsync(ReadLine readLine, string? inputText = "Test")
+    {
+        _mockTextReader.ReadLine().Returns(inputText);
+        return new ActivityTestFixture(readLine)
+            .ConfigureServices(services => services.AddSingleton(_mockProvider))
+            .ExecuteAsync();
+    }
+}