The e function runs PHP's htmlspecialchars function with the double_encode option set to true by default:
<?php echo e('<html>foo</html>');
<?php     {

        foreach (Arr::wrap($values) as $value) {

            PHPUnit::assertStringContainsString(

                $escape ? e($value): $value,

                $this->html($stripInitialData)

            );

        }
<?php     {

        foreach (Arr::wrap($values) as $value) {

            PHPUnit::assertStringNotContainsString(

                $escape ? e($value): $value,

                $this->html($stripInitialData)

            );

        }