def test_substr_from_consumed_string(self):
s = TextScanner("abcdef")
s.consume(2)
assert s.substr(2) == ""
assert s.substr(3) == "c"
assert s.substr(4) == "cd"
assert s.substr(10) == "cdef"
def test_substr_index_error(self):
with pytest.raises(IndexError):
TextScanner("").substr(-1)
s = TextScanner("abcd")
s.consume(2)
with pytest.raises(IndexError):
s.substr(1)
