> tibble(a = 1, a = 1)
Error: Column name `a` must not be duplicated.

> tibble(a = new_environment())
Error: All columns in a tibble must be vectors.
x Column `a` is an environment.

> tibble(a = 1, b = 2:3, c = 4:6, d = 7:10)
Error: Tibble columns must have compatible sizes.
* Size 2: Existing data.
* Size 3: Column `c`.
i Only values of size one are recycled.

