Thanks for the PR! While we're here, could you add a unit test that exercises the bug?

Thanks for the PR! While we're here, could you add a unit test that exercises the bug?

I need help with adding a test. I know where to add it - scipy/sparse/csgraph/tests/test_graph_laplacian.py
but I don't know whether to extend the existing tests or add a completely new one seeing this params/pattern repeated in many tests

@pytest.mark.parametrize("arr_type", [np.array,
                                      sparse.csr_matrix,
                                      sparse.coo_matrix])

cc @perimosocordiae

The arr_type parametrizing is the part of the test that should be extended. The existing _check... functions should not be affected by sparray input. And additional tests shouldn't be needed. So I think you should just add to the arr_type list with 2 more types: csr_array and coo_array. I think that shows up on lines 171, 247, 304. That should show that it breaks on the current system and is fixed by this PR.

What additional steps should be taken to get it merged or backport it to another version?

Merged. Thanks!