Assert that certain conditions are trueSource:
assert() is a drop-in replacement for
stopifnot() that supports more
informative error messages.
Any number of R expressions that return
logical(1), each of which should evaluate to
TRUE. Rather than combining expressions with
&&, separate them by commas so that better error messages can be generated.
character(1). Custom message to return.
If any of the expressions defined in
stop() is called,
producing an error message indicating the first expression which was not