Question

I have a little JUnit-Test that export an Object to the FileSystem. In the first place my test looked like this

public void exportTest {
   //...creating a list with some objects to export...    
   JAXBService service = new JAXBService();
   service.exportList(list, "output.xml");
}

Usually my test contain a assertion like assertEquals(…). So I changed the code to the following

public void exportCustomerListTest() throws Exception {
    // delete the old resulting file, so we can test for a new one at the end
    File file = new File("output.xml");
    file.delete();

    //...creating a list with some objects to export...

    JAXBService service = new JAXBService();
    service.exportCustomers(list, "output.xml");

    // Test if a file has been created and if it contains some bytes
    FileReader fis = new FileReader("output.xml");
    int firstByte = fis.read();

    assertTrue(firstByte != -1 );
}

Do I need this, or was the first approach enough? I am asking because, the first one is actually just “testing” that the code runs, but not testing any results. Or can I rely on the “contract” that if the export-method runs without an exception the test passes?

Thanks

Answer 1

Well, you’re testing that your code runs to completion without any exceptions – but you’re not testing anything about the output.

Why not keep a file with the expected output, and compare that with the actual output? Note that this would probably be easier if you had an overload of expertCustomers which took a Writer – then you could pass in a StringWriter and only write to memory. You could test that in several ways, with just a single test of the overload which takes a filename, as that would just create a FileOutputStream wrapped in an OutputStreamWriter and then call the more thoroughly tested method. You’d really just need to check that the right file existed, probably.