DirectoryInfoBase.Exists fails, and DirectoryInfoBase.ToString() behaves incorrectly

[LatteAno]

The following two unit tests fail:

	[TestInitialize]
	public void TestInit() {
		var desktopPath = Environment.ExpandEnvironmentVariables(@"%USERPROFILE%\Desktop");
		var tempDirPath = Environment.ExpandEnvironmentVariables(@"%USERPROFILE%\AppData\Local\Temp");

		IFileSystem mock = new System.IO.Abstractions.TestingHelpers.MockFileSystem(
			new Dictionary<string, MockFileData>(/*StringComparer.OrdinalIgnoreCase*/) {
				[desktopPath] = new MockDirectoryData()
			});
		IFileSystem real = new System.IO.Abstractions.FileSystem();

		real.Directory.SetCurrentDirectory(tempDirPath);
		mock.Directory.SetCurrentDirectory(tempDirPath);

		_realFileName = real.DirectoryInfo.FromDirectoryName(@"..\..\..\Desktop");
		_mockFileName = mock.DirectoryInfo.FromDirectoryName(@"..\..\..\Desktop");
	}

	[TestMethod]
	public void Test_ExistsProperty() {
		Assert.IsTrue(_realFileName.Exists); // Passed.
		Assert.IsTrue(_mockFileName.Exists); // Failed!
	}

	[TestMethod]
	public void Test_ToStringMethod() {
		Assert.AreEqual(@"..\..\..\Desktop", _realFileName.ToString()); // Passed.
		Assert.AreEqual(@"..\..\..\Desktop", _mockFileName.ToString()); // Failed!
		// mockFileName.ToString() emits: @"C:\Users\USERNAME\AppData\Desktop"
	}

[fgreinacher]

Thanks for reporting! Seems like we have room for improvement around relative path handling.