Tests fail on Python 3.6 and 3.7

[nedbat]

Like this:

=============================================================================== test session starts ===============================================================================
platform darwin -- Python 3.6.10, pytest-6.1.0, py-1.9.0, pluggy-0.13.1
cachedir: .tox/py36/.pytest_cache
rootdir: /Users/ned/scriv, configfile: setup.cfg
plugins: mock-3.3.1
collected 86 items

tests/test_collect.py .............                                                                                                                                         [ 15%]
tests/test_config.py ..........F...........                                                                                                                                 [ 40%]
tests/test_create.py ..................                                                                                                                                     [ 61%]
tests/test_format_md.py .........                                                                                                                                           [ 72%]
tests/test_format_rst.py ............                                                                                                                                       [ 86%]
tests/test_gitinfo.py .....                                                                                                                                                 [ 91%]
tests/test_literals.py FFFF..                                                                                                                                               [ 98%]
tests/test_process.py .                                                                                                                                                     [100%]

==================================================================================== FAILURES =====================================================================================
______________________________________________________________________________ test_literal_reading _______________________________________________________________________________

temp_dir = PosixPath('/private/var/folders/j2/gr3cj3jn63s5q8g3bjvw57hm0000gp/T/pytest-of-ned/pytest-7/test_literal_reading0')

    def test_literal_reading(temp_dir):
        # Any setting can be read from a literal in a file.
        (temp_dir / "sub").mkdir()
        (temp_dir / "sub" / "foob.py").write_text(
            """# comment\n__version__ = "12.34.56"\n"""
        )
>       text = Config(version="literal:sub/foob.py: __version__").version

/Users/ned/scriv/tests/test_config.py:175:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
<attrs generated init scriv.config.Config>:17: in __init__
    self.__attrs_post_init__()
/Users/ned/scriv/.tox/py36/lib/python3.6/site-packages/scriv/config.py:177: in __attrs_post_init__
    self.resolve_all()
/Users/ned/scriv/.tox/py36/lib/python3.6/site-packages/scriv/config.py:191: in resolve_all
    value = self.resolve_value(value)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = Config(fragment_directory='changelog.d', format='rst', categories=['Removed', 'Added', 'Changed', 'Deprecated', 'Fixed...date.strftime('%Y-%m-%d') }}", version='literal:sub/foob.py: __version__', main_branches=['master', 'main', 'develop'])
value = 'literal:sub/foob.py: __version__'

    def resolve_value(self, value: str) -> str:
        """
        Interpret prefixes in config files to find the actual value.

        Also, "${config:format}" is replaced with the configured
        format ("rst" or "md").

        Prefixes:
            "file:" read the content from a file.
            "literal:" read a literal string from a file.

        """
        value = value.replace("${config:format}", self.format)
        if value.startswith("file:"):
            file_name = value.partition(":")[2].strip()
            file_path = Path(self.fragment_directory) / file_name
            if file_path.exists():
                value = file_path.read_text()
            else:
                try:
                    file_bytes = pkgutil.get_data(
                        "scriv", "templates/" + file_name
                    )
                except IOError as err:
                    msg = "No such file: {}".format(file_path)
                    raise Exception(msg) from err
                assert file_bytes
                value = file_bytes.decode("utf-8")
        elif value.startswith("literal:"):
            _, file_name, literal_name = value.split(":", maxsplit=2)
            found = find_literal(file_name.strip(), literal_name.strip())
            if found is None:
>               raise Exception("Couldn't find literal: {!r}".format(value))
E               Exception: Couldn't find literal: 'literal:sub/foob.py: __version__'

/Users/ned/scriv/.tox/py36/lib/python3.6/site-packages/scriv/config.py:303: Exception
_____________________________________________________________________ test_find_python_literal[version-1.2.3] _____________________________________________________________________

name = 'version', value = '1.2.3', temp_dir = PosixPath('/private/var/folders/j2/gr3cj3jn63s5q8g3bjvw57hm0000gp/T/pytest-of-ned/pytest-7/test_find_python_literal_versi0')

    @pytest.mark.parametrize(
        "name, value",
        [
            ("version", "1.2.3"),
            ("also", "xyzzy"),
            ("but", "hello there"),
            ("somewhere_else", "this would be an odd place to get the string"),
            ("a_thing_2", None),
            ("how_many", None),
        ],
    )
    def test_find_python_literal(name, value, temp_dir):
        with open("foo.py", "w") as f:
            f.write(PYTHON_CODE)
>       assert find_literal("foo.py", name) == value
E       AssertionError: assert None == '1.2.3'
E        +  where None = find_literal('foo.py', 'version')

/Users/ned/scriv/tests/test_literals.py:48: AssertionError
______________________________________________________________________ test_find_python_literal[also-xyzzy] _______________________________________________________________________

name = 'also', value = 'xyzzy', temp_dir = PosixPath('/private/var/folders/j2/gr3cj3jn63s5q8g3bjvw57hm0000gp/T/pytest-of-ned/pytest-7/test_find_python_literal_also_0')

    @pytest.mark.parametrize(
        "name, value",
        [
            ("version", "1.2.3"),
            ("also", "xyzzy"),
            ("but", "hello there"),
            ("somewhere_else", "this would be an odd place to get the string"),
            ("a_thing_2", None),
            ("how_many", None),
        ],
    )
    def test_find_python_literal(name, value, temp_dir):
        with open("foo.py", "w") as f:
            f.write(PYTHON_CODE)
>       assert find_literal("foo.py", name) == value
E       AssertionError: assert None == 'xyzzy'
E        +  where None = find_literal('foo.py', 'also')

/Users/ned/scriv/tests/test_literals.py:48: AssertionError
____________________________________________________________________ test_find_python_literal[but-hello there] ____________________________________________________________________

name = 'but', value = 'hello there', temp_dir = PosixPath('/private/var/folders/j2/gr3cj3jn63s5q8g3bjvw57hm0000gp/T/pytest-of-ned/pytest-7/test_find_python_literal_but_h0')

    @pytest.mark.parametrize(
        "name, value",
        [
            ("version", "1.2.3"),
            ("also", "xyzzy"),
            ("but", "hello there"),
            ("somewhere_else", "this would be an odd place to get the string"),
            ("a_thing_2", None),
            ("how_many", None),
        ],
    )
    def test_find_python_literal(name, value, temp_dir):
        with open("foo.py", "w") as f:
            f.write(PYTHON_CODE)
>       assert find_literal("foo.py", name) == value
E       AssertionError: assert None == 'hello there'
E        +  where None = find_literal('foo.py', 'but')

/Users/ned/scriv/tests/test_literals.py:48: AssertionError
______________________________________________ test_find_python_literal[somewhere_else-this would be an odd place to get the string] ______________________________________________

name = 'somewhere_else', value = 'this would be an odd place to get the string'
temp_dir = PosixPath('/private/var/folders/j2/gr3cj3jn63s5q8g3bjvw57hm0000gp/T/pytest-of-ned/pytest-7/test_find_python_literal_somew0')

    @pytest.mark.parametrize(
        "name, value",
        [
            ("version", "1.2.3"),
            ("also", "xyzzy"),
            ("but", "hello there"),
            ("somewhere_else", "this would be an odd place to get the string"),
            ("a_thing_2", None),
            ("how_many", None),
        ],
    )
    def test_find_python_literal(name, value, temp_dir):
        with open("foo.py", "w") as f:
            f.write(PYTHON_CODE)
>       assert find_literal("foo.py", name) == value
E       AssertionError: assert None == 'this would be an odd place to get the string'
E        +  where None = find_literal('foo.py', 'somewhere_else')

/Users/ned/scriv/tests/test_literals.py:48: AssertionError
============================================================================= short test summary info =============================================================================
FAILED tests/test_config.py::test_literal_reading - Exception: Couldn't find literal: 'literal:sub/foob.py: __version__'
FAILED tests/test_literals.py::test_find_python_literal[version-1.2.3] - AssertionError: assert None == '1.2.3'
FAILED tests/test_literals.py::test_find_python_literal[also-xyzzy] - AssertionError: assert None == 'xyzzy'
FAILED tests/test_literals.py::test_find_python_literal[but-hello there] - AssertionError: assert None == 'hello there'
FAILED tests/test_literals.py::test_find_python_literal[somewhere_else-this would be an odd place to get the string] - AssertionError: assert None == 'this would be an odd plac...
========================================================================== 5 failed, 81 passed in 1.86s ===========================================================================
ERROR: InvocationError for command /Users/ned/scriv/.tox/py36/bin/coverage run -p -m pytest -Wd (exited with code 1)
_____________________________________________________________________________________ summary _____________________________________________________________________________________
ERROR:   py36: commands failed