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[bot]]

This is addressed in release v20.0.28.