Remove divide-by-zero causing warning in test suite

[MaxGhenis]

This warning shows up in the test suite

openfisca_us/tests/test_variables.py::test_variable[spm_unit_income_decile]
/opt/hostedtoolcache/Python/3.7.12/x64/lib/python3.7/site-packages/microdf/generic.py:253: RuntimeWarning: invalid value encountered in true_divide
ranks /= self.weights.values.sum()

[martinholmer]

@MaxGhenis, do you want pytest warnings converted to pytest failures? I'm not sure what you are proposing in issue #745.

[MaxGhenis]

@martinholmer I clarified the title: we should get rid of the divide-by-zeros.

[martinholmer]

@MaxGhenis said in issue #745:

... we should get rid of the divide-by-zeros.

That makes sense. This can be handled in several ways. The way that would focus people's attention on fixing these problems would be to convert the warnings into failures.

As I said in closed issue #1332, that can be accomplished by editing the Makefile "test" target to invoke pytest with a -W option like this:

     pytest -W error::RuntimeWarning openfisca_us/tests/ --maxfail=0

There is a complete discussion on the pytest documentation page called How to capture warnings.

Leaving things as they are now doesn't seem to have focused anybody on using the warning lines numbers to fix the divide-by-zero instances.

[MaxGhenis]

I'd hesitate to block PRs on warnings right now, since they're not hurting any results AFAIK and sometimes warnings pop up because of dependencies, but Zero Warnings seems like a good aspirational goal so that command is helpful.