@Test public void testNameOfTensDigit() { assertEquals("ten", ntn.nameOfTensDigit(1)); assertEquals("twenty", ntn.nameOfTensDigit(2)); assertEquals("thirty", ntn.nameOfTensDigit(3)); assertEquals("forty", ntn.nameOfTensDigit(4)); assertEquals("fifty", ntn.nameOfTensDigit(5)); assertEquals("sixty", ntn.nameOfTensDigit(6)); assertEquals("seventy", ntn.nameOfTensDigit(7)); assertEquals("eighty", ntn.nameOfTensDigit(8)); assertEquals("ninety", ntn.nameOfTensDigit(9)); }