Laravel: how test a route with mocked Guzzle on Controller constructor?

I would test that my method calls internal API and returns a View.

This is my Controller:

  /**
     * Create a new controller instance.
     *
     * @param mixed|null $client a Guzzle instance. No type-hint to prevent autoload
     *
     * @return void
     */
    public function __construct($client = null)
    {
        $this->middleware('auth');
        $this->middleware('user.settings');
        if ($client === null) {
            $param = [
                'base_uri' => 'http://localhost/api/v1/',
                'defaults' => [
                    'exceptions' => false,
                    'verify' => false
                ]
            ];
            $client = new Client($param);
        }
        $this->setClient($client);
    }

    /**
     * Show the application dashboard.
     *
     * @return \Illuminate\Contracts\Support\Renderable
     */
    public function dashboard(Request $request)
    {
        $user_settings = $request->get('user_settings');
        $public_ip = null;
        $response = $this->getClient()->get('public-ip');
        $json = $response->getBody()->getContents();
        $public_ip = json_decode($json,1);
        return view('v110.pages.dashboard')->with('public_ip', $public_ip)->with('user_settings', $user_settings);
    }

And this is the test

public function test_dashboard_call_guzzle_client_and_returns_public_ip()
    {
        $this->withoutExceptionHandling();
        //$this->withMiddleware(); if need I can re-enable

        $fixture = dirname(__DIR__,2).'/Fixtures/Api/public-ip-ok.json';
        $this->assertFileExists($fixture);

        $body = file_get_contents($fixture);
        $this->assertTrue(is_string($body));

        $mock = new MockHandler([
            new Response(200,array(),$body)
        ]);

        $handler = HandlerStack::create($mock);

        $client = new Client([
            'handler' => $handler,
            'base_uri' => 'http://www.example.com'
        ]);

        $data = [
            'id' => 1
        ];
        $user = factory(User::class)->make($data);
        $response = $this->actingAs($user)->get(Route('dashboard'));
        $response->assertViewIs('v110.pages.dashboard');

    }

How can I pass that $client mocked Guzzle to the Controller?

Route is defined as

Route::get('/dashboard','HomeController@dashboard')->name('dashboard');

via Chebli Mohamed