breakpoint() builtin not working with pytest

One curious feature of an activated Firedrake environment is that the Python builtin breakpoint() function no longer works when run with pytest, but the more verbose import pdb; pdb.set_trace() still does. This is caused by the Python package used for testing notebooks, nbval, and the interplay between testing for code coverage and setting breakpoints (related issue).

The standard behaviour of breakpoint() may be achieved by either uninstalling nbval (pip uninstall nbval), or disabling the nbval plugin by passing -p no:nbval to pytest on the command line.