assert_colnames         Assert that a data.frame contains specified
                        column names
assert_coltypes         Assert that a data.frame's columns are certain
                        types
assert_ids              Assert that a data.frame contains all unique
                        combinations of specified ID variables, and
                        doesn't contain duplicates within combinations
assert_nrows            Assert that a data.frame contains a specified
                        number of rows
assert_values           Assert that a data.frame's columns are
                        non-NA/infinite, or are greater, less than,
                        equal/not-equal, or contain specified values.
check_files             Check for the existence of a vector of files,
                        optionally repeated for a set amount of time.
import_files            Given a vector of filenames, append all files
                        and return as one data.table using a
                        user-defined function
