{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "# Property-based testing"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "slideshow": {
     "slide_type": "skip"
    }
   },
   "outputs": [],
   "source": [
    "from hypothesis import given, assume, example, note, settings, strategies as st\n",
    "from hypothesis.stateful import RuleBasedStateMachine, rule, invariant\n",
    "from random import randint\n",
    "from collections import Counter\n",
    "import unittest"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Motivation"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "Would you accept `plus`?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "slideshow": {
     "slide_type": "skip"
    }
   },
   "outputs": [],
   "source": [
    "def plus(x, y):\n",
    "  if x and y:\n",
    "    return 2\n",
    "  return 1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "assert plus(1, 0) == 1\n",
    "assert plus(0, 1) == 1\n",
    "assert plus(1, 1) == 2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "def plus(x, y):\n",
      "  if x and y:\n",
      "    return 2\n",
      "  return 1\n"
     ]
    }
   ],
   "source": [
    "%history 2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "slideshow": {
     "slide_type": "skip"
    }
   },
   "outputs": [],
   "source": [
    "def plus_v2(a, b):\n",
    "  return a + b"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "Would you accept `plus_v2`?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "for _ in range(1000):\n",
    "  a = randint(-100, 100)\n",
    "  b = randint(-100, 100)\n",
    "  assert plus_v2(a, b) == a + b"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "def plus_v2(a, b):\n",
      "  return a + b\n"
     ]
    }
   ],
   "source": [
    "%history 3"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "Can we test `plus_v2` without `+`?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "def associative(a, b):\n",
    "  return plus_v2(plus_v2(a, b), 1) == plus_v2(a, plus_v2(b, 1))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "def commutative(a, b):\n",
    "  return plus_v2(a, b) == plus_v2(b, a)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "def zero_is_identity(a):\n",
    "  return plus_v2(a, 0) == a"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "for _ in range(1000):\n",
    "  a = randint(-100, 100)\n",
    "  b = randint(-100, 100)\n",
    "  assert associative(a, b)\n",
    "  assert commutative(a, b)\n",
    "  assert zero_is_identity(a)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "Rewriting in Hypothesis"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "@given(a=st.integers(), b=st.integers())\n",
    "def test_plus_v2(a, b):\n",
    "  assert associative(a, b)\n",
    "  assert commutative(a, b)\n",
    "  assert zero_is_identity(a)\n",
    "  \n",
    "test_plus_v2()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "### Generating values"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "-30412"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "st.integers().example()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "-1e-05"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "st.floats().example()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "u'\\U0005423a'"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "st.text().example()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[False]"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "st.lists(st.booleans()).example()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['Context',\n",
       " 'Decimal',\n",
       " 'FloatKey',\n",
       " 'Fraction',\n",
       " 'InvalidArgument',\n",
       " 'LRUReusedCache',\n",
       " 'NOTHING',\n",
       " 'Nothing',\n",
       " 'RandomSeeder',\n",
       " 'ResolutionFailed',\n",
       " 'STRATEGY_CACHE',\n",
       " 'SearchStrategy',\n",
       " '_AVERAGE_LIST_LENGTH',\n",
       " '__all__',\n",
       " '__builtins__',\n",
       " '__doc__',\n",
       " '__file__',\n",
       " '__name__',\n",
       " '__package__',\n",
       " '_defer_from_type',\n",
       " '_strategies',\n",
       " 'absolute_import',\n",
       " 'assume',\n",
       " 'base_defines_strategy',\n",
       " 'binary',\n",
       " 'booleans',\n",
       " 'builds',\n",
       " 'cacheable',\n",
       " 'ceil',\n",
       " 'characters',\n",
       " 'check_strategy',\n",
       " 'check_type',\n",
       " 'check_valid_bound',\n",
       " 'check_valid_integer',\n",
       " 'check_valid_interval',\n",
       " 'check_valid_sizes',\n",
       " 'choices',\n",
       " 'complex_numbers',\n",
       " 'composite',\n",
       " 'convert_value',\n",
       " 'count_between_floats',\n",
       " 'data',\n",
       " 'dates',\n",
       " 'datetimes',\n",
       " 'decimals',\n",
       " 'deferred',\n",
       " 'defines_strategy',\n",
       " 'defines_strategy_with_reusable_values',\n",
       " 'dictionaries',\n",
       " 'division',\n",
       " 'dt',\n",
       " 'enum',\n",
       " 'fixed_dictionaries',\n",
       " 'float_to_int',\n",
       " 'floats',\n",
       " 'floor',\n",
       " 'fractions',\n",
       " 'from_regex',\n",
       " 'from_type',\n",
       " 'frozensets',\n",
       " 'gcd',\n",
       " 'get_type_hints',\n",
       " 'getfullargspec',\n",
       " 'hrange',\n",
       " 'implements_iterator',\n",
       " 'infer',\n",
       " 'int_to_float',\n",
       " 'integers',\n",
       " 'is_negative',\n",
       " 'isclass',\n",
       " 'isfunction',\n",
       " 'iterables',\n",
       " 'just',\n",
       " 'lists',\n",
       " 'math',\n",
       " 'none',\n",
       " 'not_set',\n",
       " 'note_deprecation',\n",
       " 'nothing',\n",
       " 'one_of',\n",
       " 'operator',\n",
       " 'permutations',\n",
       " 'print_function',\n",
       " 'proxies',\n",
       " 'random_module',\n",
       " 'randoms',\n",
       " 'recursive',\n",
       " 'reduce',\n",
       " 'register_type_strategy',\n",
       " 'renamed_arguments',\n",
       " 'required_args',\n",
       " 'runner',\n",
       " 'sampled_from',\n",
       " 'sets',\n",
       " 'shared',\n",
       " 'streaming',\n",
       " 'text',\n",
       " 'text_type',\n",
       " 'timedeltas',\n",
       " 'times',\n",
       " 'try_convert',\n",
       " 'tuples',\n",
       " 'uuids']"
      ]
     },
     "execution_count": 17,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dir(st)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "### Property-based testing patterns\n",
    "\n",
    "* \"Doesn't blow up\"\n",
    "* Encode/decode\n",
    "* Idempotence\n",
    "* Oracle"
   ]
  }
 ],
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