@Test
public void testConvert() {

    // przypadki testowe: [argument][oczekiwana wartosc holdera]
    Object[][] testCases = {
        {new Long(17), 17L},
        {new Integer(50), 50L},
        {null, null},
        {"", null},
        {" ", null},
        {"123", 123L}
    };
    // wykonanie testow
    for (Object[] testCase : testCases) {
        Object obj = testCase[0];
        Long expectedValue = (Long) testCase[1];
        ValueHolder holder = TypeDecoder.convert(type, obj);
        assertEquals(expectedValue, holder.getValue());
    }
}