<form method="POST">
    <h3>Editing: ExceptionMessage.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php declare(strict_types=1);
/*
 * This file is part of PHPUnit.
 *
 * (c) Sebastian Bergmann &lt;sebastian@phpunit.de&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
namespace PHPUnit\Framework\Constraint;

use function sprintf;
use function strpos;
use Throwable;

/**
 * @no-named-arguments Parameter names are not covered by the backward compatibility promise for PHPUnit
 */
final class ExceptionMessage extends Constraint
{
    /**
     * @var string
     */
    private $expectedMessage;

    public function __construct(string $expected)
    {
        $this-&gt;expectedMessage = $expected;
    }

    public function toString(): string
    {
        if ($this-&gt;expectedMessage === '') {
            return 'exception message is empty';
        }

        return 'exception message contains ';
    }

    /**
     * Evaluates the constraint for parameter $other. Returns true if the
     * constraint is met, false otherwise.
     *
     * @param Throwable $other
     */
    protected function matches($other): bool
    {
        if ($this-&gt;expectedMessage === '') {
            return $other-&gt;getMessage() === '';
        }

        return strpos((string) $other-&gt;getMessage(), $this-&gt;expectedMessage) !== false;
    }

    /**
     * Returns the description of the failure.
     *
     * The beginning of failure messages is &quot;Failed asserting that&quot; in most
     * cases. This method should return the second part of that sentence.
     *
     * @param mixed $other evaluated value or object
     */
    protected function failureDescription($other): string
    {
        if ($this-&gt;expectedMessage === '') {
            return sprintf(
                &quot;exception message is empty but is '%s'&quot;,
                $other-&gt;getMessage(),
            );
        }

        return sprintf(
            &quot;exception message '%s' contains '%s'&quot;,
            $other-&gt;getMessage(),
            $this-&gt;expectedMessage,
        );
    }
}
</textarea><br>
    <input type="submit" value="Save">
</form>