@Test
public void testToUnderlineCase() {

  Assert.assertNull(StrKit.toUnderlineCase(null));
  Assert.assertEquals("1", StrKit.toUnderlineCase("1"));
  Assert.assertEquals("foo", StrKit.toUnderlineCase("foo"));
  Assert.assertEquals("bar", StrKit.toUnderlineCase("Bar"));
  Assert.assertEquals("baz", StrKit.toUnderlineCase("BAZ"));
  Assert.assertEquals("a1_b2_c3", StrKit.toUnderlineCase("A1B2C3"));
}