phpunit failed

[araneta]

I tried to run phpunit . from the root of this code ( /home/aldo/projects/university/apps/rest-server/silex/) but i got this error:
PHP Fatal error: Class 'Monolog\TestCase' not found in /home/aldo/projects/university/apps/rest-server/silex/vendor/monolog/monolog/tests/Monolog/Formatter/FlowdockFormatterTest.php on line 18
here is my conf

<?xml version="1.0" encoding="UTF-8"?>

<phpunit
    backupGlobals               = "false"
    backupStaticAttributes      = "false"
    colors                      = "true"
    convertErrorsToExceptions   = "true"
    convertNoticesToExceptions  = "true"
    convertWarningsToExceptions = "true"
    processIsolation            = "false"
    stopOnFailure               = "false"
    syntaxCheck                 = "false"
    bootstrap                   = "vendor/autoload.php">

    <testsuites>
        <testsuite name="Test Suite">
            <directory>src/</directory>
            <directory>tests/</directory>
        </testsuite>
    </testsuites>

</phpunit>