Added missing test for get_spacings

[fziegner]

This PR addresses #425 and adds a test for the get_spacings function.

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[github-actions]

Linting results by Pylint:

Your code has been rated at 8.69/10 (previous run: 8.69/10, +0.00)
_{The linting score is an indicator that reflects how well your code version follows Pylint’s coding standards and quality metrics with respect to the RC_v1.5.x branch.
A decrease usually indicates your new code does not fully meet style guidelines or has potential errors.}

[fsenf]

@fziegner : Thank you! The test looks good and runs smoothly. It is ready to be merged!