group-map.md
In dplyr: A Grammar of Data Manipulation

group_map() give meaningful errors

Code
  (expect_error(mtcars %>% group_by(cyl) %>% group_modify(~ data.frame(cyl = 19)))
  )
Output
  <error/rlang_error>
  Error in `group_modify()`:
  ! The returned data frame cannot contain the original grouping variables: cyl.
Code
  (expect_error(mtcars %>% group_by(cyl) %>% group_modify(~10)))
Output
  <error/rlang_error>
  Error in `group_modify()`:
  ! The result of `.f` must be a data frame.
Code
  (expect_error(iris %>% group_by(Species) %>% group_modify(head1)))
Output
  <error/rlang_error>
  Error in `group_modify()`:
  ! `.f` must accept at least two arguments.
  i You can use `...` to absorb unused components.
Code
  (expect_error(iris %>% group_by(Species) %>% group_map(head1)))
Output
  <error/rlang_error>
  Error in `group_map()`:
  ! `.f` must accept at least two arguments.
  i You can use `...` to absorb unused components.