Add more unit tests

[brosaplanella]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• [ ] New feature (non-breaking change which adds functionality)
• [ ] Optimization (back-end change that speeds up the code)
• [ ] Bug fix (non-breaking change which fixes an issue)

Key checklist

• [ ] No style issues: $ python -m nox -s lint
• [ ] All tests pass: $ python -m nox -s unit examples integration
• [ ] Coverage is complete $ python -m nox -s coverage
• [ ] The documentation builds: $ python -m nox -s sphinx

Further checks

• [ ] Code is commented, particularly in hard-to-understand areas
• [ ] Tests added that prove fix is effective or that feature works

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (ec5b64a) 9.02% compared to head (1a4ea0f) 21.06%. Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5 +/- ## ========================================== + Coverage 9.02% 21.06% +12.03% ========================================== Files 7 7 Lines 432 432 ========================================== + Hits 39 91 +52 + Misses 393 341 -52 ``` [see 1 file with indirect coverage changes](https://app.codecov.io/gh/paramm-team/data_processing/pull/5/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=paramm-team)

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