CSV阅读器的模拟和单元测试

Question

Does it make sense to mock in unit test of a csv reader where we want to read the csv and put them into POJOs and make some queries? (specifically I mean mocking file read).

Let's assume the following example:

 ICsvBeanReader beanReader = null;
    beanReader = new CsvBeanReader(new FileReader(csvFileName),
            CsvPreference.STANDARD_PREFERENCE);
    String[] header = beanReader.getHeader(true);
    Book bookBean = null;
    while ((bookBean = beanReader.read(Book.class, header,
         processors))!= null) {
     books.add(bookBean);
    }

Thank you in advance.

Answer 1

This seems like a good idea - it can decouple your unit being tested from your implementation of read(). That way if you change to a different library to read the files, your unit tests don't all have to be rewritten.

Answer 2

Strictly speaking, a unit test is designed to test the functionality of a piece of code, rather than the integration of code with an external part of the program. Testing the functionality of reading an actual file would be an integration test, rather than a unit test. An integration test is important too, because you want to make sure that your file reader can function on actual files. But for the purpose of ensuring that the code runs, you can also create a unit test.

To create a unit test, you can mock the file reader object to return a dummy response ( byte[] or whatever type the interface provides). Then you can populate your POJOs and do your assertions that everything behaves as expected.

So to summarize, both an integration test and a unit test might be a good idea, but a unit test will allow you to isolate and test the logic of your code.

Update:

To take your updated code sample into account, I would go about mocking the CsvBeanReader like this:

ICsvBeanReader mockedBeanReader = mock(CsvBeanReader.class);
Book book1 = new Book();
Book book2 = new Book();
Book book3 = new Book();
when(mockedBeanReader.getHeader(true))
    .thenReturn(new String[]{"here", "is", "header"});
when(mockedBeanReader.read(Book.class, header, processors))
    .thenReturn(book1)
    .thenReturn(book2)
    .thenReturn(book3);

And now you have a fully mocked CsvBeanReader object. You can perform assertions on your POJOs and verify that the business logic of your code be correct.