def patchUserDatabase(patch, user, uid, group, gid):
    """
    Patch L{pwd.getpwnam} so that it behaves as though only one user exists
    and patch L{grp.getgrnam} so that it behaves as though only one group
    exists.

    @param patch: A function like L{TestCase.patch} which will be used to
        install the fake implementations.

    @type user: C{str}
    @param user: The name of the single user which will exist.

    @type uid: C{int}
    @param uid: The UID of the single user which will exist.

    @type group: C{str}
    @param group: The name of the single user which will exist.

    @type gid: C{int}
    @param gid: The GID of the single group which will exist.
    """
    # Try not to be an unverified fake, but try not to depend on quirks of
    # the system either (eg, run as a process with a uid and gid which
    # equal each other, and so doesn't reliably test that uid is used where
    # uid should be used and gid is used where gid should be used). -exarkun
    pwent = pwd.getpwuid(os.getuid())
    grent = grp.getgrgid(os.getgid())

    database = UserDatabase()
    database.addUser(
        user, pwent.pw_passwd, uid, gid,
        pwent.pw_gecos, pwent.pw_dir, pwent.pw_shell)

    def getgrnam(name):
        result = list(grent)
        result[result.index(grent.gr_name)] = group
        result[result.index(grent.gr_gid)] = gid
        result = tuple(result)
        return {group: result}[name]

    patch(pwd, "getpwnam", database.getpwnam)
    patch(grp, "getgrnam", getgrnam)
    patch(pwd, "getpwuid", database.getpwuid)

    Patch L{pwd.getpwnam} so that it behaves as though only one user exists
    and patch L{grp.getgrnam} so that it behaves as though only one group
    exists.

    @param patch: A function like L{TestCase.patch} which will be used to
        install the fake implementations.

    @type user: C{str}
    @param user: The name of the single user which will exist.

    @type uid: C{int}
    @param uid: The UID of the single user which will exist.

    @type group: C{str}
    @param group: The name of the single user which will exist.

    @type gid: C{int}
    @param gid: The GID of the single group which will exist.
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_twistd.py