Fix time overlap handling in concatenation

[zklaus]

Description

Closes #2248

Link to documentation:

---

Before you get started

• ☝ Create an issue to discuss what you are going to do

Checklist

It is the responsibility of the author to make sure the pull request is ready to review. The icons indicate whether the item will be subject to the 🛠 Technical or 🧪 Scientific review.

• 🧪 The new functionality is relevant and scientifically sound
• 🛠 This pull request has a descriptive title and labels
• 🛠 Code is written according to the code quality guidelines
• 🧪 and 🛠 Documentation is available
• 🛠 Unit tests have been added
• 🛠 Changes are backward compatible
• 🛠 Any changed dependencies have been added or removed correctly
• 🛠 The list of authors is up to date
• 🛠 All checks below this pull request were successful

---

To help with the number pull requests:

• 🙏 We kindly ask you to review two other open pull requests in this repository

[codecov]

Codecov Report

Merging #2247 (962a367) into main (f39d14a) will decrease coverage by 0.01%.
The diff coverage is 97.87%.

@@            Coverage Diff             @@
##             main    #2247      +/-   ##
==========================================
- Coverage   93.47%   93.47%   -0.01%     
==========================================
  Files         238      238              
  Lines       12917    12932      +15     
==========================================
+ Hits        12074    12088      +14     
- Misses        843      844       +1     

Files	Coverage Δ
esmvalcore/preprocessor/_io.py	90.69% <97.87%> (+0.16%)	⬆️

[zklaus]

The coverage fails only due to one line, the special case when the passed cube list is shorter than two (i.e. has zero or one entries), in which case the function returns the input cube list unmodified. This is not covered by tests because the test works at the level of the concatenate function, which performs this check before, thus even though concatenate is tested with an empty cube list, this does not reach _check_time_overlaps.

There are two possible solutions: Add a test for _check_time_overlaps itself or remove the check inside the function, taking it as a guarantee by the caller. A third approach is to ignore the code coverage deterioration.

What do the reviewers think?

[bouweandela]

Looks good to me!

[valeriupredoi]

well you can mock the concatenate func with that single cube, but nay bother, if Bouwe is OK with that am too 👍

[valeriupredoi]

plus 97.87% is pretty much 100% in my books 😁

[valeriupredoi]

very nice refactoring @zklaus - many thanks! I added M2.10 to it since I reckon it's good to have it in the bugfix bit of the release - feel free to remove it if you think we should wait 🍺