env.py

quoted = lambda s: '"' + str.replace(s, '"', '\\"') + '"'
unquoted = lambda s: str.replace(s[1:-1], '\\"', '"')

slash = lambda s: str.replace(s, '\\', '\\\\')
unslash = lambda s: str.replace(s, '\\\\', '\\')

shell_escape = lambda s: quoted(slash(s))
shell_unescape = lambda s: unslash(unquoted(s))

test_env.py

from env import *
from hypothesis import given
import hypothesis.strategies as st


@given(st.text())
def test_quoted_serialization(s):
    assert s == unquoted(quoted(s))


@given(st.text())
def test_slash_serialization(s):
    assert s == unslash(slash(s))


@given(st.text())
def test_shell_escape_serialization(s):
    assert s == shell_unescape(shell_escape(s))


if __name__ == '__main__':
    test_quoted_serialization()
    test_slash_serialization()
    test_shell_escape_serialization()