How to write a test that checks for insufficient space available?

[FroggieFrog]

Describe the bug
I need to write a test for some logic that checks if there is enough space available on disk.

To Reproduce

logic to test

private IFileSystem _fileSystem;//injected in ctor as = new MockFileSystem() in tests | = new FileSystem() in production

var requiredSpace = calculateActualSize(filePaths);
var availableFreeSpace = getAvailableFreeSpaceOnDisk(driveName);
if (availableFreeSpace < requiredSpace)
{
 //throw exception
}

private long getAvailableFreeSpaceOnDisk(string driveName)
{
 var driveInfo = _fileSystem.DriveInfo.FromDriveName(driveName);
 var result = driveInfo.AvailableFreeSpace;
 return result;
}

test code so far (does not work)

[Fact]
public void RequiredSpaceIsInsufficient_ShouldThrow()
{
 // Arrange
 var fileSystem = new MockFileSystem(); 
 fileSystem.AddDirectory(@"Q:\Destination");
 fileSystem.AddFile(@"W:\source\test.txt", new MockFileData(new byte[2]));

 var driveInfo = new MockDriveInfo(fileSystem, "Q");
 driveInfo.AvailableFreeSpace = 1;

 // Act 
 var ex = Record.Exception(() => new ClassToTest(fileSystem).MethodToTest());

 // Assert
 Assert.IsType<ExpectedExceptionType>(ex);
}

Actual behavior
The injected IFileSystem has a DriveInfo with AvailableFreeSpace set to 0.

Expected behavior
The injected IFileSystem has a DriveInfo with AvailableFreeSpace set to 1.

Additional context
I did some search and found a comment on issue #274, but I'm still unable to understand how to write a functioning test.

[fgreinacher]

This is currently not possible. As mentioned in the issue you linked these properties should actually be read-only.

Would be cool to support this somehow, but I guess it would be quite some effort. I will probably not find the time for implementing this anytime soon, but would be open for a contribution.

[FroggieFrog]

Thank you for your time and your reply.
In the meantime I managed to come up with a workaround.
I made my own IFileSystem by inheriting from MockFileSystem and used Moq. Maybe it is useful for someone else.

public class TestClass
{
 [Fact]
 public void CreateBackup_RequiredSpaceIsInsufficient_ShouldReturnFalse()
 {
 // Arrange
 var sourceFilePath = $@"A:\source\test.txt";
 var fileSize = 2;

 //setup DriveInfo for backup
 var mockedDriveInfo = new Mock<IDriveInfo>();
 mockedDriveInfo.Setup(x => x.Name).Returns(() => "Q");
 mockedDriveInfo.Setup(x => x.AvailableFreeSpace).Returns(() => fileSize - 1);

 var mockedDriveInfoFactory = new Mock<IDriveInfoFactory>();
 mockedDriveInfoFactory.Setup(x => x.FromDriveName(It.IsAny<string>())).Returns(() => mockedDriveInfo.Object);

 //add files to backup to FileSystem
 var fileSystem = new MyMockFileSystem(mockedDriveInfoFactory.Object);
 fileSystem.AddFile(sourceFilePath, new MockFileData(new byte[fileSize]));

 // ...
 }
}

internal class MyMockFileSystem : MockFileSystem
{
 private IDriveInfoFactory _driveInfoFactory;

 public MyMockFileSystem(IDriveInfoFactory driveInfoFactoryToUse) : base()
 {
 _driveInfoFactory = driveInfoFactoryToUse;
 }

 public override IDriveInfoFactory DriveInfo => _driveInfoFactory;
}

[fgreinacher]

In the meantime I managed to come up with a workaround. I made my own IFileSystem by inheriting from MockFileSystem and used Moq. Maybe it is useful for someone else.

Thanks for sharing your solution, looks neat to me!

[github-actions]

This is addressed in release v20.0.28.