Daillyn,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
$( ".box" ).each(function(i, box) {
$(box).on('mouseenter', '.box__case', function (event) {
const index = $('.box__case', box).index(this),
text = [1,2,3,"test"][index];
$('.box__title', box).text(text);
});
});
});
</script>
</head>
<body>
<div class="box">
<h3 class="box__title"></h3>
<p class="box__case">Text_1</p>
<p class="box__case">Text_2</p>
<p class="box__case">Text_3</p>
<p class="box__case">Text_4</p>
</div>
</body>
</html>