@Override public SlotAssignmentResult ensure(long key1, long key2) {
        assert key1 != unassignedSentinel : "ensure() called with key1 == nullKey1 (" + unassignedSentinel + ')';
        return super.ensure0(key1, key2);
    }
@Test
    public void testCursor_advance_afterAdvanceReturnsFalse() {
        hsa.ensure(randomKey(), randomKey());

        HashSlotCursor16byteKey cursor = hsa.cursor();
        cursor.advance();
        cursor.advance();

        assertThrows(AssertionError.class, cursor::advance);
    }