 with <code>_not</code> that returns a message if the condition is not met.</p>
<p><code><a href="reference/messagehandler.html">stop_if_not()</a></code> is quite the same as <code>assert_that()</code> from the {assertthat} package, except that it can takes mappers. It is not the same as base <code>stopifnot()</code>, as it doesn’t take a list of expression.</p>
<p>These functions are also flexible as you can pass base predicates (is.numeric, is.character…), a custom predicate built with mappers, or eve