anchor.diff:  module test_helpers
   
     use iso_c_binding, only: c_double, c_bool
  -  use helpers, only: cross_product, vector_close, in_interval
  +  use helpers, only: cross_product, bbox, vector_close, in_interval
     use types, only: dp
     implicit none
     private test_cross_product, test_vector_close, test_in_interval
  
positive.code: 
    end subroutine test_cross_product
  
    subroutine test_vector_close(success)
      logical(c_bool), intent(inout) :: success
      ! Variables outside of signature.
  
negative.code:     logical(c_bool), intent(inout) :: success
  
      call test_cross_product(success)
      call test_bbox(success)
      call test_vector_close(success)
      call test_in_interval(success)
  
  