PHPUnit test

Code:

In Class
function validate($key){
  $session = \Config\Services::session($config);
  //more code
}

In Test Class
function testvalidate(){
      $key = "example_key";
      $result = $class->validate($key);
      $this->assertEquals(true, $result);
}

Execute test:
Error: ErrorException: Undefined variable: config

Code:

how can I set the $config variable?

Code:

  $session = \Config\Services::session($config);

Why do you need $config?

Code:

$session = \Config\Services::session();

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