fail("Null value should raise IllegalArgument");
} catch (IllegalArgumentException e) {
// expected
}
assertEquals("First key should be A", map.firstKey(), "A");
assertEquals("Last key should be C", map.lastKey(), "C");
assertEquals("First key in tail map should be B",
map.tailMap("B").firstKey(), "B");
assertEquals("Last key in head map should be B",
map.headMap("C").lastKey(), "B");
assertEquals("Last key in submap should be B",