how to use hypothesis to generate "valid" passwords

password_checker_test.py

import random
import string

from hypothesis import given
from hypothesis import settings
from hypothesis import strategies as st

import password_checker


def is_password_good(password):
    return password_checker.is_password_good('jrheard', '12345', password)


def test_too_short_rejected():
    assert is_password_good('z$6') == False


def test_containing_student_info_is_bad():
    assert is_password_good('carlsJrHeard!') == False
    assert is_password_good('Hi there! 12345') == False


def test_exactly_eight_characters():
    assert is_password_good('abc123!@') == True


def test_two_categories_not_enough():
    assert is_password_good('1234abcd') == False
    assert is_password_good('ABCDabcd') == False
    assert is_password_good('!!!!aaaa') == False
    assert is_password_good('!!!AAA!A') == False


def test_three_categories_is_good():
    assert is_password_good('abc123!@') == True
    assert is_password_good('abcABC123') == True
    assert is_password_good('!@#ABCabc') == True


VALID_PASSWORD_CHARACTERS = (
    string.ascii_lowercase
    + string.ascii_uppercase
    + string.digits
    + string.punctuation
)


short_password_strategy = st.text(alphabet=VALID_PASSWORD_CHARACTERS, max_size=7)


@given(short_password=short_password_strategy)
def test_too_short_rejected_via_hypothesis(short_password):
    assert is_password_good(short_password) == False


@st.composite
def valid_password_composite(draw):
    """Generates valid passwords to be given to the student's password checker.
    See https://hypothesis.readthedocs.io/en/latest/data.html#composite-strategies.
    """
    # Valid passwords can contain 3 or 4 categories of character.
    num_categories_present = random.randint(3, 4)
    booleans = [True] * num_categories_present

    if num_categories_present == 3:
        booleans.append(False)

    random.shuffle(booleans)

    contains_lowercase, contains_uppercase, contains_digits, contains_symbols = booleans

    strategies = []
    if contains_lowercase:
        strategies.append(draw(st.text(alphabet=string.ascii_lowercase, min_size=1)))
    if contains_uppercase:
        strategies.append(draw(st.text(alphabet=string.ascii_uppercase, min_size=1)))
    if contains_digits:
        strategies.append(draw(st.text(alphabet=string.digits, min_size=1)))
    if contains_symbols:
        strategies.append(draw(st.text(alphabet=string.punctuation, min_size=1)))

    password = list(''.join(strategies))
    random.shuffle(password)
    return ''.join(password)


valid_passwords = valid_password_composite().filter(lambda s: len(s) >= 8)


def doesnt_contain_student_info(password):
    return '12345' not in password and 'jrheard' not in password


passwords_without_student_info = valid_passwords.filter(doesnt_contain_student_info)


@settings(max_examples=2000)
@given(password=passwords_without_student_info)
def test_long_enough_passwords_are_good(password):
    assert is_password_good(password) == True