Guard TestOutputHelper.WriteLine calls against lifetime exceptions

[Copilot]

Fix XUnit TestOutputHelper Lifetime Issue ✅

• Analyze the issue - XUnit TestOutputHelper lifetime problem
• Understand root cause - TestOutputHelper captured in closures outlives test lifetime
• Create Helpers.fs with centralized safeWriteLine function
• Update PropertyAttribute.fs to use Helpers.safeWriteLine
• Update CheckExtensions.fs to use Helpers.safeWriteLine
• Update Runner.fs to use Helpers.safeWriteLine
• Move tests to F# in FsCheck.Test project
• Fix Directory.Packages.props - Remove implicit ReferenceAssemblies package
• Build FsCheck.Xunit successfully
• Verify all tests pass (11 XUnit tests including 5 new lifetime tests)
• Complete

Solution Implemented:
Created a centralized Helpers module with a single safeWriteLine function that wraps TestOutputHelper.WriteLine() calls in try-catch blocks to handle InvalidOperationException when the test has completed and the helper is no longer active. This prevents the error "There is no currently active test" when closures that capture the TestOutputHelper are called after the test lifetime ends.

Root Cause:
The TestOutputHelper was being captured in closures for the Every and EveryShrink callbacks when verbose mode is enabled. These closures can outlive the test's lifetime, especially when tests run in parallel or sequentially. When XUnit 2.9.0+ introduced stricter lifetime management for TestOutputHelper, these lingering references would throw InvalidOperationException when accessed.

Test Results:

• Created 5 comprehensive F# tests in PropertyAttributeTests.fs:
  • 2 Property tests with parameters to generate multiple test cases
  • 1 Verbose Property test that specifically exercises Every and EveryShrink callbacks
  • 2 Fact tests for mixed test scenarios
• All 11 XUnit tests pass consistently
• No regressions detected

Files Changed:

• src/FsCheck.Xunit/Helpers.fs - New internal module with centralized safeWriteLine helper
• src/FsCheck.Xunit/FsCheck.Xunit.fsproj - Added Helpers.fs to compilation order
• src/FsCheck.Xunit/PropertyAttribute.fs - Updated to use Helpers.safeWriteLine
• src/FsCheck.Xunit/CheckExtensions.fs - Updated to use Helpers.safeWriteLine
• src/FsCheck.Xunit/Runner.fs - Updated to use Helpers.safeWriteLine
• tests/FsCheck.Test/Fscheck.XUnit/PropertyAttributeTests.fs - Added F# lifetime tests
• Directory.Packages.props - Removed implicit Microsoft.NETFramework.ReferenceAssemblies package reference

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Lifetime problem with Xunit: InvalidOperationException: There is no currently active test.</issue_title>
<issue_description>I get reproducable runtime error on one of two tests if I run all tests of the following test class / project. If I run just one test (e.g. manually in IDE Rider) everything looks good (no error).

Just guessing: maybe related to #657

Exception

System.InvalidOperationException: There is no currently active test.

System.InvalidOperationException
There is no currently active test.
   at Xunit.Sdk.TestOutputHelper.GuardInitialized() in /_/src/xunit.execution/Sdk/Frameworks/TestOutputHelper.cs:line 52
   at Xunit.Sdk.TestOutputHelper.QueueTestOutput(String output) in /_/src/xunit.execution/Sdk/Frameworks/TestOutputHelper.cs:line 61
   at Xunit.Sdk.TestOutputHelper.WriteLine(String message) in /_/src/xunit.execution/Sdk/Frameworks/TestOutputHelper.cs:line 109
   at TestProject1.UnitTest1.Test2() in TestProject1\UnitTest1.cs:line 18
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

Here is my C# project:

UnitTest1.cs

public class UnitTest1(Xunit.Abstractions.ITestOutputHelper testOutputHelper)
{
    [FsCheck.Xunit.Property]
    public void Test1()
    {
        testOutputHelper.WriteLine($"{nameof(Test1)}");
    }

    [Xunit.Fact]
    public void Test2()
    {
        testOutputHelper.WriteLine($"{nameof(Test2)}");
    }
}

TestProject1.csproj

<Project Sdk="Microsoft.NET.Sdk">
    <PropertyGroup>
        <TargetFramework>net8.0</TargetFramework>
        <IsTestProject>true</IsTestProject>
    </PropertyGroup>
    <ItemGroup>
        <PackageReference Include="FsCheck.Xunit" Version="3.0.0" />
        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
        <PackageReference Include="xunit" Version="2.9.3" />
        <PackageReference Include="xunit.runner.visualstudio" Version="3.0.1" />
    </ItemGroup>
</Project>

Reproducable by just running dotnet test in project folder.

No error if I downgrade to xunit 2.8.1 / FsCheck.Xunit 2.16.6.

<Project Sdk="Microsoft.NET.Sdk">
    <PropertyGroup>
        <TargetFramework>net8.0</TargetFramework>
        <IsTestProject>true</IsTestProject>
    </PropertyGroup>
    <ItemGroup>
        <PackageReference Include="FsCheck.Xunit" Version="2.16.6" />
        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
        <PackageReference Include="xunit" Version="2.8.1" />
        <PackageReference Include="xunit.runner.visualstudio" Version="3.0.1" />
    </ItemGroup>
</Project>
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@kurtschelfthout</author><body>
I can't reproduce this...</body></comment_new>
<comment_new><author>@kurtschelfthout</author><body>
The testoutputhelper is suspicious. xunit has a bit of rough edges around handling it - see the comments in the code in the xUnit Property attribute in FsCheck.Xunit. Perhaps it's related to that.</body></comment_new>
</comments>

• Fixes Lifetime problem with Xunit: InvalidOperationException: There is no currently active test. #692

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[kurtschelfthout]

• Add a new file/internal module called Helpers, add safeWriteLine there once, and call that function from everywhere.
• move the tests to FsCheck.Test and write them in F#

[Copilot]

• Add a new file/internal module called Helpers, add safeWriteLine there once, and call that function from everywhere.
• move the tests to FsCheck.Test and write them in F#

Done in commit 81dad6e:

• Created Helpers.fs with a single internal safeWriteLine function
• Updated PropertyAttribute.fs, CheckExtensions.fs, and Runner.fs to call the centralized helper
• Moved tests from C# to F# in PropertyAttributeTests.fs with 5 test cases (2 Property, 1 Verbose Property, 2 Fact)
• All 11 XUnit tests pass