test: minor fixes to notebook/script tests

[wpbonelli]

• prevent potential None reference
• add comment re: collection order
• reformat test scripts

[codecov]

Codecov Report

Merging #1862 (283f349) into develop (6475074) will not change coverage.
The diff coverage is n/a.

❗ Current head 283f349 differs from pull request most recent head e601e9a. Consider uploading reports for the commit e601e9a to get more accurate results

@@           Coverage Diff           @@
##           develop   #1862   +/-   ##
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  Coverage     72.2%   72.2%           
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  Files          256     256           
  Lines        56112   56112           
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  Hits         40564   40564           
  Misses       15548   15548