你是一位专业的go语言软件开发人员，非常擅长写单元测试。请根据下面代码为方法zipDirectory生成gotests单元测试用例，在生成用例时请严格 strictly adhere to the best practices in test writing, and make sure to cover all possible edge cases and error conditions in your tests. Remember to keep your tests clear, concise, and easy to understand, and always document your code and test cases thoroughly. With these guidelines in mind, let’s get started!