How to use the habanero.cn.content_negotiation function in habanero

def test_content_negotiation_alt_url():
    "content negotiation - alternative url"
    res = cn.content_negotiation(ids = '10.1126/science.169.3946.635', url = "http://doi.org")
    assert str == str(res).__class__

def test_content_negotiation_raises_an_http_error_with_bad_requests():
    "content negotiation - raises an HTTPError with bad requests"
    res = cn.content_negotiation(ids = '10.1126/foo')

"""
    parsed_refs = []
    for ref in refs:
        if ref in _REFERENCE_CACHE:
            parsed_ref = _REFERENCE_CACHE[ref]
        elif ref.startswith('@'):
            parsed_ref = ref
        elif ref.startswith('url:'):
            # uses arbitrary key
            url = ref.split('url:')[1]
            parsed_ref = """@misc{{url:{0},
                       url = {{{1}}}
                       }}""".format(str(abs(url.__hash__()))[0:6], url)
        elif ref.startswith('doi:'):
            doi = ref.split('doi:')[1]
            parsed_ref = content_negotiation(doi, format='bibentry')
        elif ref.startswith('isbn:'):
            isbn = ref.split('isbn:')[1]
            parsed_ref = bibformatters['bibtex'](meta(isbn))
        else:
            raise ValueError('Unknown reference style for '
                             'reference: {} (please either '
                             'supply a BibTeX string, or a string '
                             'starting with url: followed by a URL or '
                             'starting with doi: followed by a DOI)'.format(ref))

        if check_if_valid_citation:
            try:
                _ = references_to_markdown(parsed_ref)
            except Exception as ex:
                raise ValueError("Reference '{}' returned the following error.\n"
                                 "You may need to manually generate a bibtex string:\n"

self.logger.debug(
                    f"Retrieved {len(refs)} formatted references from Crossref."
                )
                md = "  \n\n".join(
                    f"> [{refs[doi]}](https://dx.doi.org/{doi}) "
                    f"Cited by {dois_to_item[doi]['cited-by']}."
                    for doi in sorted_dois
                )
                formatted_references = dcc.Markdown(md, className="mpc-markdown")

            else:
                # else retrieve BibTeX entries to extract a nice author list
                # and perform our own formatting

                entries = {
                    doi: content_negotiation(ids=doi, format="bibtex")
                    for doi in sorted_dois
                }

                formatted_entries = []
                for doi, entry in entries.items():
                    author_string = self._bibtex_entry_to_author_text(entry)
                    journal_div = self._item_to_journal_div(dois_to_item[doi])

                    formatted_entries.append(
                        html.Blockquote(
                            [
                                html.A(
                                    [
                                        html.Div(
                                            [
                                                html.I(