custom error handler: this phpunit test fails. Why? (PHP7)

I'm studying PHP and, meanwhile, writing toy code to understand what I study.

These are my "error and exception handler" functions.

My intention is:

• to convert any "old style" PHP error in an Exception
• to display the Exception
• to log an error message in the syslog

function display_exception($exception)
{
    print_r($exception);
}

function log_error_or_exception($error_type, $error_message, $error_number = null, $file_name = null, $line_number = null)
{

    $text = 'Message: ' . $error_message . ' - ErrorType: ' . $error_type;

    if ($error_number) {
        $text .= ' - Error#: ' . $error_number;
    }
    if ($file_name) {
        $text .= ' -> ' . $file_name;
    }
    if ($line_number) {
        $text .= ':' . $line_number;
    }

    syslog(LOG_ERR, $text);
}


/**
 * This function logs any uncaught exception that has been thrown. 
 * If in the "dev" environment it also displays the Exception
 *
 * @var  Exception $exception
 * @return void
 */
function custom_exception_handler($exception)
{
    if (ENV == 'dev') {
        display_exception($exception);
    }

    log_error_or_exception(get_class($exception), $exception->getMessage(), $exception->getCode(), $exception->getFile(), $exception->getLine());
}

/**
 * This function converts an "old style" PHP Error in an ErrorException
 * 
 * @var  int  $errno
 * @var  string  $errstr
 * @var  string|null  $errfile
 * @var  int|null  $errline
 * @var  array $errcontext
 * @return false|void
 */
function custom_error_handler(int $errno, string $errstr, string $errfile = null, int $errline = null, array $errcontext = array())
{
    // if error_reporting() is false it means that the error was trigger by a line having
    // the error control operator "@" so the error should never be displayed.
    // Sometimes thought it's convenient to log it
    if (!error_reporting()) {
        if (ENV == 'dev') {
            log_error_or_exception('Error', $errstr, $errno, $errfile, $errline);
        }
        return false;
    }

    throw new ErrorException($errstr, $errno, 1, $errfile, $errline);
    echo "this should not be displayed";
}

set_exception_handler('custom_exception_handler');
set_error_handler('custom_error_handler');

Now I have an object

<?php

require_once 'app/src/ErrorExceptionHandlers.php';

class Obj
{
    public function method($value){
        $result = preg_match('/@/', $value);
    }
}

If I run this code everything works as expected:

define('ENV', 'dev');

$object = new Obj;
$object->method(array());

I get:

ErrorException Object
(
    [message:protected] => preg_match() expects parameter 2 to be string, array given
    [string:Exception:private] => 
    ...
)

If I try to run this phpunit test

<?php

require_once 'app/src/models/obj.php';

define('ENV', 'dev');

class ObjTest extends \PHPUnit_Framework_TestCase
{
    /**
     * @ExpectedException ErrorException
     */
    public function test_method(){
        $object = new Obj();
        $object->method(array());
    }
}

I get:

There was 1 error:

1) ObjTest::test_method
ErrorException: preg_match() expects parameter 2 to be string, array given

Why does the test fail?