> # One column
> vars_rename(c("a", "b", "c"), b = a)
Error: Names must be unique.

> # Multiple columns
> vars_rename(c("a", "b", "c", "d"), c = a, d = b)
Error: Names must be unique.

> # Overlapping rename with one duplicate column
> vars_rename(c("a", "b", "c"), b = a, c = b)
Error: Names must be unique.

