def test_add_discard(self):
        """
        Check that the insertion logic does not create an infinite lookup
        chain with deleted entries (insertion should happen at the first
        deleted entry, not at the free entry at the end of the chain).
        See issue #1913.
        """
        pyfunc = add_discard_usecase
        check = self.unordered_checker(pyfunc)

        # ensure a and b are different
        a = b = None
        while a == b:
            a, b = self.sparse_array(2)
        check((a,), b, b)

        Check that the insertion logic does not create an infinite lookup
        chain with deleted entries (insertion should happen at the first
        deleted entry, not at the free entry at the end of the chain).
        See issue #1913.
        
numba/tests/test_sets.py