Testing file input streams in java

Question

@Override
public Collection<Flight> getAll() {
    try (ObjectInputStream ois = new ObjectInputStream(new BufferedInputStream(new FileInputStream(file)))) {
        Object read = ois.readObject();
        List<Flight> objects   = (ArrayList<Flight>) read;
        return objects;
    } catch (IOException | ClassNotFoundException ex) {
        ex.printStackTrace();
        return new ArrayList<>();
    }
}

@Test
public void testGetAll() {
    try (ObjectInputStream ois = new ObjectInputStream(new BufferedInputStream(new FileInputStream("flights.txt")))) {
        Object read = ois.readObject();
        expected = (ArrayList<Flight>) read;
    } catch (IOException | ClassNotFoundException ex) {
        ex.printStackTrace();
    }
    Collection<Flight> actual = flightService.getAll();
    assertEquals(expected, actual);
}

Hi I have serious problem with testing. Is the above code a correct way to test? Please help me

No, that's not a good way to test it; it duplicates the code rather than setting up a proper environment where the result is predictable and then checking that. Where does the file come from in the getAll() method? — daniu
– daniu, Commented Mar 13, 2020 at 7:31
Yah i felt it, it is wrong(.... getAll() got file from same place which Collection<Flight> get.. Both take file form "flights.txt" — Samir Allahverdi
– Samir Allahverdi, Commented Mar 13, 2020 at 7:32
What I meant is, how is file initialized in the tested class. Is the file path passed to it, or is it some constant value. — daniu
– daniu, Commented Mar 13, 2020 at 7:51
i dont initialize any file in tested class.there is one file which located in project.and I read these file in both case (expected and actual). Should I initilaze new file in test class? — Samir Allahverdi
– Samir Allahverdi, Commented Mar 13, 2020 at 8:00
I don't mean the file itself, I mean the file variable (containing the file path). Is it passed to the class in a constructor or set via some method? — daniu
– daniu, Commented Mar 13, 2020 at 8:19

daniu · Accepted Answer · 2020-03-13 09:31:58Z

1

So say your class is given the file to read in the constructor, like this:

class FlightReader {
    File file;
    public FlightReader(File f) {
        file = f;
    }
    // your getAll here
}

then a test would first create a file of its own with known data, then read it, then verify the results are as expected, like this:

@Test
public void testGetAll() {
    Flight f1 = new Flight("ACREG1", "B737");
    Flight f2 = new Flight("ACREG2", "A320");
    Flight f3 = new Flight("ACREG3", "B777");
    List<Flight> written = new ArrayList<>(Arrays.asList(f1, f2, f3));
    File tempFile = File.createTempFile("flights", "test");
    // write sample data
    try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(tempFile))) {
        oos.writeObject(written);
    }

    // data is written to a file, read it back using the tested code
    FlightReader reader = new FlightReader(tempFile);
    List<Flight> readFlights = reader.getAll();

    // verify the written and read data are the same
    assertThat(readFlights).contains(f1, f2, f3);
}

Some notes:

you should use specific classes - like in this case ArrayList - as little as possible. Why cast to an ArrayList if you just return a Collection in the end?
you shouldn't use Java Serialization at all; it's error-prone, a security risk, and considered a mistake by the Java architects.

edited Mar 13, 2020 at 9:31

answered Mar 13, 2020 at 8:54

daniu

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5 Comments

Samir Allahverdi Over a year ago

So it can create another file

Samir Allahverdi Over a year ago

and we will read this file ,and check if getall contains correct object yes?

Samir Allahverdi Over a year ago

What is FlightReader here?

daniu Over a year ago

@SamirAllahverdiyev FlightReader is the name I gave your class to be tested since you didn't mention it. The Flight class needs a properly defined equals () method for this to work.

Samir Allahverdi Over a year ago

Yeap I get it Thanksss

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