def test_leaves():
t = TableSymbol('t', '{id: int32, name: string}')
v = TableSymbol('v', '{id: int32, city: string}')
x = ScalarSymbol('x', 'int32')
assert t.leaves() == [t]
assert t.id.leaves() == [t]
assert by(t.name, t.id.nunique()).leaves() == [t]
assert join(t, v).leaves() == [t, v]
assert join(v, t).leaves() == [v, t]
assert (x + 1).leaves() == [x]
