def METHOD_NAME(self, tmp_path):
    path = tmp_path / "doc.json"
    doc = FileMappedDocument(path)
    doc["number"] = 42
    doc["nested"] = {"foo": "bar"}
    doc.save()
    doc = FileMappedDocument(path)
    doc.load()
    assert doc == {"number": 42, "nested": {"foo": "bar"}}