lsp-mode: How do I figure out the code responsible for "run test" pop ups?

In lsp-mode+gopls you can get "run test" buttons next to your tests. Very nice, but how do I discover the source code for it? Obviously C-h k and C-h f doesn't work. C-h mouse-click to get docs about whatever element I click on would be nice to have :-).

Put point on one of them and try `C-u C-x =`. That will show the text properties for the character at point. One of those properties should be a function; either the one you're looking for or one that leads there.

C-h k *normally* works on mouse clicks.

The code for lenses is located in `lsp-lens.el`.