Run testthat tests with a filter argument as the first one and allow running in parallel using a flag

test_file.R

.test_file <- function(file = NULL, use_parallel = FALSE) {
  if (use_parallel) {
    testthat::with_mocked_bindings(
      devtools::test(filter = file),
      find_parallel = function(...) {
        TRUE
      },
      .package = "testthat"
    )
  }
  devtools::test(filter = file)
}