Do you mind checking out from github so that we can have tests included?

looks like they can be found here: https://github.com/ResidentMario/missingno/blob/master/tests

they are important to ensure your package wont be broken by upstream dependencies, and I find that most science related packages like to break often.

I found that integrating tests here initiates a snowball effect, where python packages are used for tests that are not (yet) in nixos. Dunno how integrating the tests of this missingno package will justify this. Thus, we can either ignore those tests, or alternatively, do not merge this package.

the pypi package didn't contain tests, I would do:

{ lib
, buildPythonPackage
, fetchFromGitHub
, matplotlib
, scipy
, seaborn
, pytest
}:

buildPythonPackage rec {
  pname = "missingno";
  version = "0.4.2";

  src = fetchFromGitHub {
    owner = "ResidentMario";
    repo = pname;
    rev = version;
    sha256 = "0wxhj7qm2fcaiprdjfrx9p8nikc10qhivf7rzwi04r6mrzyi0i9x";
  };

  propagatedBuildInputs = [
    matplotlib
    scipy
    seaborn
  ];

  checkInputs = [ pytest ];
  checkPhase = ''
    pytest tests/util_tests.py -k 'not cutoff'
  '';

  meta = with lib; {
    description = "Missing data visualization module for Python.";
    homepage = https://github.com/ResidentMario/missingno;
    maintainers = with maintainers; [ msigl ];
    license = licenses.mit;
  };
}

Ah ok. Naively I did assume that we have to run all tests. According to this packages' contributing guidelines there are two types of tests. Namely the visualizing tests tests/viz_tests.py and utility tests tests/util_tests.py.
For those viz-tests additional data is needed, which is loaded via quilt - a data versioning system for AWS. However, this quilt is not in nixos as some other dependencies of quilt are also not in nixos.
Long story short: sure, we can only do the utility tests as you suggested.

yea, those looked very involved.

We more or less just want to verify that the package is in a valid state. Util tests should give us some code coverage

Indentation + missing hooks, see https://github.com/jtojnar/nixpkgs-hammering/blob/master/explanations/explicit-phases.md .

Also pytestCheckHook is prefered.