Last week, I created #14967 for implementation of plotting methods. Soon after pushing my commits, many of the jobs failed on Travis. It was strange as I was not able to reciprocate the errors locally.
After discussing it on Gitter, I got to know that it was due to the printing of plots using TextBackend in the doctest in absence of matplotlib. As matplotlib was present in my system, doctest used matplotlib backend instead of TextBackend locally, hence passing all tests. Kalevi suggested using unset_show to stop the printing of plots during doctest but apparently, unset_show didn’t work for TextBackend. This was fixed by #14984 later that day and #14967 passed all the tests after former one was merged.
This week, I also started editing #14453 for documentation. It included a few beam problems along with their ascii diagrams.