assertEquals doesn't show errors when the test is expecting exceptions

Question

I recently started to work with Junit.

I have a function that receives a line with values taken from a txt file, and returns instances with that values.

Everytime that function receives wrong values, I throw an exception.

My test method is verifying if the exceptions are working fine, and if the values returned by the instance are right.

@Test(expected = StudentException.class)
public void testImportStudent() {
    String txtline = "1, Name, Name"; //Wrong, It should be 1, Name
    Source test = studentMain.importStudent(txtline); //Throw error
    txtline = "1, Name"; //Right
    test = percursoGestor.importSource(line); //Test passed
    assertEquals("Error inserting ID", 3, test.getStudentID()); //Test ignores this line
    assertEquals("Error inserting Name", "Nothing", test.getStudentName()); //Test ignores this line
}

So, my test checks if the error was thrown, but ignores the assertequals, even though I put a value different than expected, the test passes. Because I'm expecting for an exception to be thrown.

What am I doing wrong?

Answer 1

You have annotated your test method with expected = StudentException.class.

What this basically does is putting a try-catch block around your whole method:

@Test(expected = StudentException.class)
public void testImportStudent() {
    try {
        String txtline = "1, Name, Name";
        Source test = studentMain.importStudent(txtline); //Throw error
        txtline = "1, Name";
        test = percursoGestor.importSource(line);
        assertEquals("Error inserting ID", 3, test.getStudentID());
        assertEquals("Error inserting Name", "Nothing", test.getStudentName());
    } catch (Exception e) {
        // verify exception
    }
}

And as usually: Nothing is executed after an exception is thrown.

The clean way would be to have two separate methods:

@Test(expected = StudentException.class)
public void testImportStudent_incorrectInput() {
    String txtline = "1, Name, Name";
    Source test = studentMain.importStudent(txtline);
}

@Test
public void testImportStudent_correctInput() {
    String txtline = "1, Name";
    Source test = percursoGestor.importSource(line);
    assertEquals("Error inserting ID", 3, test.getStudentID());
    assertEquals("Error inserting Name", "Nothing", test.getStudentName());    
}

If you really want to test multiple cases in one method (which you probably don't), then you can work with try-catch yourself:

@Test
public void testImportStudent() {
    String txtline = "1, Name, Name";
    Source test;
    try {
        test = studentMain.importStudent(txtline);
        // Make sure that the test fails when no exception is thrown
        fail();
    } catch (Exception e) {
        // Check for the correct exception type
        assertTrue(e instanceof StudentException);
    }
    // Other checks
    txtline = "1, Name";
    test = percursoGestor.importSource(line);
    assertEquals("Error inserting ID", 3, test.getStudentID());
    assertEquals("Error inserting Name", "Nothing", test.getStudentName());
}