def test_combine():
x = Locus('1',1,2)
y = Locus('1',3,4)
z = x.combine(y)
assert z.start == 1
assert z.end == 4
assert len(z.children) == 2
def test_combine_chromosome_mismatch():
x = Locus('1',1,2)
y = Locus('2',3,4)
with pytest.raises(ChromosomeError):
z = x.combine(y)
