Measure the test coverage

[yakutovicha]

fixes #440

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@ca48cc4). Click here to learn what that means. Patch has no changes to coverable lines.

:exclamation: Current head 18094f5 differs from pull request most recent head 322ea71. Consider uploading reports for the commit 322ea71 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #441 +/- ## ========================================= Coverage ? 39.21% ========================================= Files ? 18 Lines ? 3091 Branches ? 0 ========================================= Hits ? 1212 Misses ? 1879 Partials ? 0 ``` | Flag | Coverage Δ | | |---|---|---| | python-3.10 | `39.21% <0.00%> (?)` | | | python-3.8 | `39.22% <0.00%> (?)` | | | python-3.9 | `39.22% <0.00%> (?)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab#carryforward-flags-in-the-pull-request-comment) to find out more. Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab)

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[yakutovicha]

Since the reported coverage is well beyond my original goal of 10-15% (as stated in the issue), I am making this PR ready for the review.

[danielhollas]

@unkcpz @yakutovicha this is great, thanks! :clap: