ImagineHelperTest error

Running plugin test with PHP 5.4.9, CakePHP 2.3.6 and PHPUnit: 3.7.19, I get the following error:

    Running ImagineHelperTest
    PHPUnit_Framework_Error_Notice
    Declaration of ImagineHelper::url() should be compatible with Helper::url($url = NULL, $full = false)
    Test case: ImagineHelperTest(testUrl)
    Stack trace:
    /.../app/Plugin/Imagine/View/Helper/ImagineHelper.php : 19
    /.../lib/Cake/Core/App.php : 563
    App::load
    /.../app/Plugin/Imagine/Test/Case/View/Helper/ImagineHelperTest.php : 31
    /usr/share/php/PHPUnit/Framework/TestCase.php : 828
    /usr/share/php/PHPUnit/Framework/TestResult.php : 648
    /usr/share/php/PHPUnit/Framework/TestCase.php : 776
    /.../lib/Cake/TestSuite/CakeTestCase.php : 84
    /usr/share/php/PHPUnit/Framework/TestSuite.php : 775
    /usr/share/php/PHPUnit/Framework/TestSuite.php : 745
    /usr/share/php/PHPUnit/TextUI/TestRunner.php : 349
    /.../lib/Cake/TestSuite/CakeTestRunner.php : 63
    /.../lib/Cake/TestSuite/CakeTestSuiteCommand.php : 115
    /.../lib/Cake/TestSuite/CakeTestSuiteDispatcher.php : 247
    /.../lib/Cake/TestSuite/CakeTestSuiteDispatcher.php : 100
    /.../lib/Cake/TestSuite/CakeTestSuiteDispatcher.php : 117
    /.../app/webroot/test.php : 98

The solution suggested here changes the order of the arguments in the url method, so maybe it is not that great for backward compatibility...