Unclear error message if matrix is used

[FlorianSeitz]

https://github.com/JanaJarecki/cognitivemodels/blob/dd3ab9757f1c25a5373f8acd29fe5a841165d6a6/tests/testthat/test_ebmj.R#L205

I get the following error:
Error in private$get_input(f = self$formulaCriterion, d = d, na.action = NULL) :
Can't find variables from 'formula' in 'data': [c].

This error seems a bit counterintuitive as we only use a matrix rather than a data frame.