public void GetChildFilePath()
        {
            // Setup
            var directory = new DirectoryInfo(@"C:\Directory");

            // Execute
            var path = directory.FilePath("File");

            // Assert
            Assert.AreEqual(@"C:\Directory\File", path);
        }
        public void GetChildFilePathWithNullFileName()
        {
            // Setup
            var directory = new DirectoryInfo(@"C:\Directory");

            // Execute
            var path = directory.FilePath(a_fileName: null);
        }