Will go through all the R files in a package, looking for instances of `testFrom` on roxygen2 `param` values in function definitions. Once it finds these, it'll expand a grid of all possibilities. This will provide a shortlist of all options to test the code with, although it will not know if the input combination should fail or pass, and if it does pass it should have a certain value.
testMatrixMaker()
will dump out a character vector of expressions suitable to be paired with their testthat expectations.
This function is a bit brittle for now. It assumes that the `testFrom` placement will be the last thing on param lines.