FakeFileSystem throws on linux, when it is created on a Windows FakeEnvironment

[nils-a]

Prerequisites

• I have written a descriptive issue title
• I have searched issues to ensure it has not already been reported

Cake runner

Cake .NET Tool

Cake version

4.0.0

Operating system

Linux

Operating system architecture

64-Bit

CI Server

No response

What are you seeing?

demo code

using Cake.Core;
using Cake.Core.IO;
using Cake.Testing;
using Xunit;

namespace test1;

public class Tests
{
    [Fact]
    public void T1()
    {
        var fixture = new MyFixture();
        
        Assert.True(fixture.FileSystem.GetDirectory(fixture.Environment.WorkingDirectory).Exists);
    }
}

public class MyFixture
{
    public ICakeEnvironment Environment { get; }
    public IFileSystem FileSystem { get; }

    public MyFixture()
    {
        Environment = FakeEnvironment.CreateWindowsEnvironment();
        FileSystem = new FakeFileSystem(Environment);
    }
}

error

System.ArgumentException: Working directory cannot be relative.

System.ArgumentException
Working directory cannot be relative.
   at Cake.Testing.FakeFileSystemTree..ctor(ICakeEnvironment environment)
   at Cake.Testing.FakeFileSystem..ctor(ICakeEnvironment environment)
   at test1.MyFixture..ctor() in /home/nils/dev/test1/Class1.cs:line 27
   at test1.Tests.T1() in /home/nils/dev/test1/Class1.cs:line 13
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

What is expected?

I expect no error to occur.

Steps to Reproduce

• Create a new project
• Add references
  • Cake.Testing
  • Microsoft.NET.Test.Sdk
  • xunit
• Use the code from above
• run the test

Output log

No response

[nils-a]

Cause of the problem:

When the FakeFileSystem is created, it creates a FakeFileSystemTree using the given ICakeEnvironment:

cake/src/Cake.Testing/FakeFileSystem.cs

Line 23 in 06e82a7

_tree = new FakeFileSystemTree(environment);

The FakeFileSystemTree checks whether environment.WorkingDirectory.IsRelative is true and if so, it throws the exception:

cake/src/Cake.Testing/FakeFileSystemTree.cs

Lines 31 to 34 in 06e82a7

	if (environment.WorkingDirectory.IsRelative)
	{
	throw new ArgumentException("Working directory cannot be relative.");
	}

Now, ICakeEnvironment.WorkingDirectory.IsRelative is defined as:

cake/src/Cake.Core/IO/Path.cs

Line 98 in 06e82a7

IsRelative = !PathHelper.IsPathRooted(FullPath);

PathHelper.IsPathRooted relies on

cake/src/Cake.Core/IO/PathHelper.cs

Line 13 in 06e82a7

private static readonly bool _isWindows = EnvironmentHelper.GetPlatformFamily() == PlatformFamily.Windows;

And EnvironmentHelper.GetPlatformFamily in turn checks, what the current system is. I.e. the system running the test, not the FakeEnvironment that was defined in the test.

Thus, the WorkingDirectory, which is defined in FakeEnvironment as

cake/src/Cake.Testing/FakeEnvironment.cs

Line 86 in 06e82a7

environment.WorkingDirectory = new DirectoryPath("C:/Working");

is checked for IsRooted on my linux system, and not on the FakeEnvironment.

On my linux system, C:/Working is not rooted. Thus, it is treated as relative, and the exception is thrown.