I wanted to catch if any TinyMce buttons were not functioning as expected, i.e. if we had Behat for Spell Check button we could have caught it sooner, although, if formatting sections and alignments sections are tightly coupled then we can reduce the test to a single behavior check on one of items in each?

I technically am just going through all buttons (in default install), to be thorough. 

I see an ultimate goal here would we can use these tests to create feature documentation using pickles https://github.com/picklesdoc/pickles, so having all functionality tested results in better docs :)

Either way, can you let me know what HTML editor tests you feel are valuable, I'll just write the ones up you specify so i'm not creating too much overhead.