check_outcomes_are_univariate() returns a named list of two components,
ok and n_cols.
Validation
hardhat provides validation functions at two levels.
check_*(): check a condition, and return a list. The list
always contains at least one element, ok, a logical that specifies if the
check passed. Each check also has check specific elements in the returned
list that can be used to construct meaningful error messages.
validate_*(): check a condition, and error if it does not pass. These
functions call their corresponding check function, and
then provide a default error message. If you, as a developer, want a
different error message, then call the check_*() function yourself,
and provide your own validation function.
Details
The expected way to use this validation function is to supply it the
$outcomes element of the result of a call to mold().