@Test
public void testNameOfTeens() {
assertEquals("ten", ntn.nameOfTeens(10));
assertEquals("eleven", ntn.nameOfTeens(11));
assertEquals("twelve", ntn.nameOfTeens(12));
assertEquals("thirteen", ntn.nameOfTeens(13));
assertEquals("fourteen", ntn.nameOfTeens(14));
assertEquals("fifteen", ntn.nameOfTeens(15));
assertEquals("sixteen", ntn.nameOfTeens(16));
assertEquals("seventeen", ntn.nameOfTeens(17));
assertEquals("eighteen", ntn.nameOfTeens(18));
assertEquals("nineteen", ntn.nameOfTeens(19));
}