Question

I am trying to test a method that copies a source file to a dest file using JUnit’s TemporaryFolder. I get a Java IOException when I try run this test however. Does it matter where I make the declaration for the folder? (My test class has several different tests in it). And if so, what is the proper way to do it? I ask because I currently have several unit tests above this code, then I try to set up the testing for the file copying. Maybe the @Rule–@Before–@Test block needs to be in its own class? Here is the snippet where I have coded the test:

...other tests...then:

@Rule
public static TemporaryFolder tmp = new TemporaryFolder();
private File f1, f2;

@Before
public void createTestData() throws IOException {
    f1 = tmp.newFile("src.txt");
    f2 = tmp.newFile("dest.txt");

    BufferedWriter out = new BufferedWriter(new FileWriter(f1));
    out.write("This should generate some \n" +
            "test data that will be used in \n" +
            "the following method.");
    out.close();
}

@Test
public void copyFileTest() {

    out.println("file 1 length: " + f1.length());
    try {
        copyFile(f1, f2);
    } catch (IOException e) {
        e.getMessage();
        e.printStackTrace();
    }

    if (f1.length() != f2.length())
        fail();
    else if (!f1.equals(f2))
        fail();
    assertSame(f1, f2);
}

When I run this test class, all 11 of my tests now fail (which previously passed) and I get java.io.IOException: No such file or directory.

Answer 1

So looking at the JUnit Javadoc, I have found out that any declaration under @Rule must be public, and not static. So I took out the static and just have:

@Rule
public TemporaryFolder tmp = new TemporaryFolder();

I still do not know for sure if it matters where this declaration is made when you have other unit tests in your class that do not use the @Rule declaration, but this did allow me to run through my tests successfully.