Exercise serializing `NoneType` values with Python's `toml`, `tomlkit`, and `tomli-w` packages

test_toml_nonetype.py

"""
About
=====

Exercise serializing `NoneType` values with Python's `toml`, `tomlkit`, and `tomli-w` packages.
Currently, it croaks with both `tomlkit` and `tomli-w`:

- `tomlkit==0.11.4`: `ValueError: Invalid type <class 'NoneType'>`
- `tomli-w==1.0.0`: `TypeError: Object of type <class 'NoneType'> is not TOML serializable`


Evaluation
==========

First of all, there is no `NULL` value in TOML, and there never will be.

- https://github.com/toml-lang/toml/issues/921
- https://twitter.com/mitsuhiko/status/1346455555435593729

While `tomli-w` still writes the file until the exception is raised, `tomlkit`
just writes an empty file. Only `toml` ignores `NoneType` values and just
skips them.


Usage
=====
::

    # Install
    pip install pytest toml tomlkit tomli-w

    # Invoke
    pytest test_toml_nonetype.py


References
==========

- https://github.com/isarengineering/SecPi/issues/25
- https://github.com/isarengineering/SecPi/pull/27
- https://github.com/sdispater/tomlkit/issues/240
- https://github.com/hukkin/tomli-w/issues/39

"""
import pytest
import toml
import tomli_w
import tomlkit

DATA_IN = {"foo": 42, "bar": None, "baz": "qux"}
TOML_OUT = 'foo = 42\nbaz = "qux"'


@pytest.mark.parametrize("module", [toml, tomlkit])
def test_write(tmp_path, module):
    filename = tmp_path.joinpath("test.toml")
    with open(filename, "w") as config_file:
        try:
            module.dump(DATA_IN, config_file)
        except Exception:
            pass
    with open(filename, "r") as config_file:
        payload = config_file.read().strip()
        assert payload == TOML_OUT


def test_write_tomli(tmp_path):
    """
    `tomli-w` needs file handle to be opened in binary mode.
    """
    filename = tmp_path.joinpath("test.toml")
    with open(filename, "wb") as config_file:
        try:
            tomli_w.dump(DATA_IN, config_file)
        except Exception:
            pass
    with open(filename, "r") as config_file:
        payload = config_file.read().strip()
        assert payload == TOML_OUT