mathlib3

879cb474 - feat(test/integration): add examples of computing integrals by simp (#6859)

feat(test/integration): add examples of computing integrals by simp (#6859) As suggested in [#6216 (comment)](https://github.com/leanprover-community/mathlib/pull/6216#discussion_r580389848). The examples added here were made possible by #6216, #6334, #6357, #6597.