Add sphinxcontrib-sphinx test for missing reference

[chrisjsewell]

@mtiley I have tried to replicate your issue in #95, but I do not find this issue.

Can you try using this fork, to run:

$ pytest tests/test_sphinx/test_sphinx_builds.py::test_bibtex_norefs

and let me know if it passes. If it does pass, then maybe try to have a look at the test I have written, and see if you can alter it to fail with your issue.
You may want to take a look at https://myst-parser.readthedocs.io/en/latest/develop/test_infrastructure.html#test-tools re: pytest-regressions.

[chrisjsewell]

If you didn't know, to use this branch do:

git clone https://github.com/ExecutableBookProject/MyST-Parser
cd MyST-Parser
git checkout fix-bibtex-95-rebase
pip install -e .[sphinx,code_style,testing,rtd]

[chrisjsewell]

In b26aa42, I've tried adding documents that might replicate your issue in the documentation:

• https://208-240151150-gh.circle-artifacts.com/0/html/bibtex_test/example_rst.html

• https://208-240151150-gh.circle-artifacts.com/0/html/bibtex_test/example_md.html

• https://230-240151150-gh.circle-artifacts.com/0/html/bibtex_test/example_rst.html

• https://230-240151150-gh.circle-artifacts.com/0/html/bibtex_test/example_md.html

I don't see your issue,
but @choldgraf this has caused some crazy formatting issues; with the top of pages not showing, and the next/previous buttons not rendered correctly. How have I done that!?

[chrisjsewell]

but @choldgraf this has caused some crazy formatting issues; with the top of pages not showing, and the next/previous buttons not rendered correctly. How have I done that!?

Ah my bad, I hadn't added --keep-going to make html-strict, to make sure the build still completes on warnings, but returns a non-zero exit code. (Was sure I'd added this but obviously not!)