Runlegth encoding tested via hypothesis

runlength.py

#!/usr/local/bin/python3.6
# -*- coding: utf-8 -*-
from hypothesis import given, example
import hypothesis.strategies as st

def decode(l):
  s = ""
  for i, c in l:
    s += i * c
  return s

@given(s=st.text())
def trivial(s):
  assert decode([(1, c) for c in s]) == s

def encode(s):
  """Run length encoding of s as a list of tuples [(repeats, character)]"""
  raise NotImplementedError

@given(s=st.text())
def round_trip(s):
  enc = encode(s)
  dec = decode(enc)
  assert s == dec, "{} != {} == decode({}) == decode(encode({}))".format(s, dec, enc, s)

@given(s=st.text())
def no_adjacent(s):
  last = None
  enc = encode(s)
  for i, c in enc:
    assert last != c, "{} == {}".format(last, c)
    last = c


if __name__ == '__main__':
  trivial()
  round_trip()
  no_adjacent()