Howdy,
So from here: https://fenicsproject.org/qa/7415/question-concerning-the-number-of-integration-points/
It seems that integration is gauss quadrature with n=3? I just wanted to verify this - since I would think 2 point quadrature would be the default.
The default behavior is to automatically estimate an appropriate quadrature degree and choose the minimum number of points needed to attain that degree. If the integrand is strictly polynomial, this will be exact, but some integrands (e.g., transcendental functions, ratios of polynomials, etc.) rely on heuristics. Note that this degree is the degree up to which polynomials are integrated exactly, not the number of quadrature points.
The default value of 3 that Miroslav mentioned in the old forum is for the degree_rise parameter to the function errornorm, which determines how much higher the polynomial degree of the space used to interpolate the exact solution should be than the approximate solution. It is only indirectly related to quadrature in the sense that it will increase the estimated quadrature degree for the integral evaluated by errornorm.