Expand test for parameter uncertainties

[alexander-held]

Question

I was looking through #1183 and noticed that there does not seem to be a test to check the values of parameter uncertainties returned by minuit, which I would expect to be done here:

pyhf/tests/test_optim.py

Lines 384 to 408 in a33badd

	@pytest.mark.parametrize('mu', [1.0], ids=['mu=1'])
	@pytest.mark.only_numpy_minuit
	def test_optim_uncerts(backend, source, spec, mu):
	pdf = pyhf.Model(spec)
	data = source['bindata']['data'] + pdf.config.auxdata
	init_pars = pdf.config.suggested_init()
	par_bounds = pdf.config.suggested_bounds()
	optim = pyhf.optimizer
	result = optim.minimize(pyhf.infer.mle.twice_nll, data, pdf, init_pars, par_bounds)
	assert pyhf.tensorlib.tolist(result)
	result = optim.minimize(
	pyhf.infer.mle.twice_nll,
	data,
	pdf,
	init_pars,
	par_bounds,
	[(pdf.config.poi_index, mu)],
	return_uncertainties=True,
	)
	assert result.shape[1] == 2
	assert pyhf.tensorlib.tolist(result)

I am happy to prepare a PR to add such a test, but wanted to check first whether this is of interest. I noticed it since that PR adds a HESSE call, which should slightly change the reported uncertainties, but did not find a corresponding change in the test.

Relevant Issues and Pull Requests

#1183

[lukasheinrich]

I think more test coverage is always better. this way we can keep track when things change

[matthewfeickert]

@alexander-held Yeah I'll second that. A PR is very welcome.