如何测试这段代码？

Question

 1：internal static void CleanUpFile(string directory, string fileName)
        {
            if (!Directory.Exists(directory))
            {
                Directory.CreateDirectory(directory);
                return;
            }
            String[] files = Directory.GetFiles(directory, fileName);
            foreach (String file in files)
            {
                File.Delete(file);
            }
        }
2  internal static void WriteCSharpSourceCode(CodeNamespace codeNameSpace, string file)
        {
            CodeGeneratorOptions options = new CodeGeneratorOptions();
            options.BlankLinesBetweenMembers = true;
            options.ElseOnClosing = true;
            options.VerbatimOrder = true;            WriteCSharpSourceCode(codeNameSpace, file, options);
        }        internal static void WriteCSharpSourceCode(CodeNamespace codeNameSpace, string file,
            CodeGeneratorOptions options)
        {
            DirectoryInfo direcotry = new FileInfo(file).Directory;
            if (!direcotry.Exists)
            {
                CreateDirectory(direcotry);
            }
            if (File.Exists(file))
            {
                File.Delete(file); // replace
            }
            Console.WriteLine(String.Format("Writing to file {0}...", file));            using (var writer = new StringWriter())
            {
                new CSharpCodeProvider().GenerateCodeFromNamespace(codeNameSpace, writer, options);
                String code = writer.GetStringBuilder().ToString();
                File.WriteAllText(file, code);
            }
        }3  internal static CodeNamespace GenClass(string spaceName, string className, string baseType, string[] imports, string comment)
        {
            CodeNamespace codeNameSpace = new CodeNamespace(spaceName);
            codeNameSpace.Comments.Add(new CodeCommentStatement(comment));
            if (imports != null)
            {
                foreach (string s in imports)
                {
                    codeNameSpace.Imports.Add(new CodeNamespaceImport(s));
                }
            }
            CodeTypeDeclaration clazzDecl = new CodeTypeDeclaration(className);
            clazzDecl.IsClass = true;
            codeNameSpace.Types.Add(clazzDecl);            if (baseType != null)
            {
                clazzDecl.BaseTypes.Add(baseType);
            }
            clazzDecl.Attributes = MemberAttributes.Public;
            return codeNameSpace;
        }请问如何写一个测试类去测试那些方法？高手有代码指导下？谢谢！
就是这种测试类：但是我测试第一个方法时候就有问题，为什么？
    [TestFixture]
    public class TestGenCodeUtil
    {
        [Test]
        public void TestCleanUpFile()
        {
            string file = @"..\tmp\A.txt";
            string directory="C";
            GenCodeUtil.CleanUpFile(directory,file);
        }
    }

Answer 1

单体测试正确值-》正确结果边界值 
错误值 然后看结果