Fix broken tests

[BjarkeHautop]

Removes the test that expects an error "there is no package called", since I can't make that trigger (and it's not from our codebase)? When I run as_caugi(obj_tidy) I get this:

> as_caugi(obj_tidy, class = "DAG")
Error in UseMethod("as.igraph") : 
  no applicable method for 'as.igraph' applied to an object of class "tidygraph"
Called from: tidygraph::as.igraph(x)

Mocked the console width in the print with truncation test, so it works even if the user has a large console size (like me). Hence, I added withr as a suggested dependency to do this.

Closes #242.