> df <- tibble(x = 1, y = 2)
> df %>% group_by(unknown)
Error: Must group by variables found in `.data`.
* Column `unknown` is not found.

> df %>% ungroup(x)
Error: `...` is not empty.

We detected these problematic arguments:
* `..1`

These dots only exist to allow future extensions and should be empty.
Did you misspecify an argument?

> df %>% group_by(x, y) %>% ungroup(z)
Error: Can't subset columns that don't exist.
x Column `z` doesn't exist.

> df %>% group_by(z = a + 1)
Error: Problem adding computed columns in `group_by()`.
x Problem with `mutate()` input `z`.
x object 'a' not found
i Input `z` is `a + 1`.

