NoMatchingExpectationException with Mockery and no idea why

i am trying to write some unit tests for my web application. I use Laravel 5.3 and Mockery.

After five hours of bashing my head against a wall, i ask for some help.

This is the simplified code:

public function saveUserWithGeneratedPassword($user, $companyId, $isAdmin)
{
    try {
        $user['password'] = $this->encryptUserPassword($this->createPassword());
        return $this->userRepository->saveUser($user, $companyId, $isAdmin);
    } catch (\Exception $e) {
        Log::error(
            'Exception occured while trying to create new user: ' . $e->__toString()
        );
        return false;
    }
}

This is the Testcode:

class UserPasswordResetTest extends TestCase {
    private $userService;

    public function setUp()
    {

        parent::setUp();

        $this->user = Mockery::mock('Eloquent', User::class)
            ->makePartial();

        $this->userRepository = Mockery::mock(IUserRepository::class);
        $this->app->instance(IUserRepository::class, $this->userRepository);

        $this->userRepository->shouldReceive('saveUser')
            ->withArgs(
                [
                    'userData',
                    'companyId',
                    'isAdmin'
                ]
            )
            ->andReturn($this->user);


        $this->userService = new UserService($this->userRepository, $this->passwordResetRepository);
    }

    public function tearDown()
    {
        parent::tearDown();
        Mockery::close();
    }

    public function testSaveUserWithGeneratedPassword()
    {
        $userData = [
            'first_name' => 'firstname',
            'last_name'  => 'lastname',
            'phone'      => '0123456789',
            'mobile'     => '0123456789',
            'locale'     => 'en',
            'email'      => 'best_email@ever.com',
            'is_active'  => '1',
            'password'   => 'password'
        ];

        $companyId = "1";
        $isAdmin = "0";


        $result = $this->userService->saveUserWithGeneratedPassword($userData, $companyId, $isAdmin);
        $this->assertInstanceOf(User::class, $result);
        $this->assertInternalType("string", $result->password);
    }
}

This is the exception:

Mockery\Exception\NoMatchingExpectationException: No matching handler found for Mockery_... Either the method was unexpected or its arguments matched no expected argument list for this method

Stack trace:
0 /home/vagrant/Code/colo21-core/vendor/mockery/mockery/library/Mockery/Loader/EvalLoader.php(16) : eval()'d code(683): Mockery\ExpectationDirector->call(Array)
1 /home/vagrant/Code/colo21-core/vendor/mockery/mockery/library/Mockery/Loader/EvalLoader.php(16) : eval()'d code(761): Mockery_3_App_Contracts_IUserRepository->_mockery_handleMethodCall('saveUser', Array)
2 /home/vagrant/Code/colo21-core/app/Services/UserService.php(122): Mockery_3_App_Contracts_IUserRepository->saveUser(Array, '1', '0')
3 /home/vagrant/Code/colo21-core/tests/UserPasswordResetTest.php(116): App\Services\UserService->saveUserWithGeneratedPassword(Array, '1', '0')
4 [internal function]: UserPasswordResetTest->testSaveUserWithGeneratedPassword()
5 /home/vagrant/Code/colo21-core/vendor/phpunit/phpunit/src/Framework/TestCase.php(1103): ReflectionMethod->invokeArgs(Object(UserPasswordResetTest), Array)
6 /home/vagrant/Code/colo21-core/vendor/phpunit/phpunit/src/Framework/TestCase.php(954): PHPUnit_Framework_TestCase->runTest()
7 /home/vagrant/Code/colo21-core/vendor/phpunit/phpunit/src/Framework/TestResult.php(701): PHPUnit_Framework_TestCase->runBare()
8 /home/vagrant/Code/colo21-core/vendor/phpunit/phpunit/src/Framework/TestCase.php(909): PHPUnit_Framework_TestResult->run(Object(UserPasswordResetTest))
9 /home/vagrant/Code/colo21-core/vendor/phpunit/phpunit/src/Framework/TestSuite.php(728): PHPUnit_Framework_TestCase->run(Object(PHPUnit_Framework_TestResult))
10 /home/vagrant/Code/colo21-core/vendor/phpunit/phpunit/src/TextUI/TestRunner.php(487): PHPUnit_Framework_TestSuite->run(Object(PHPUnit_Framework_TestResult))
11 /home/vagrant/Code/colo21-core/vendor/phpunit/phpunit/src/TextUI/Command.php(188): PHPUnit_TextUI_TestRunner->doRun(Object(PHPUnit_Framework_TestSuite), Array, true)
12 /home/vagrant/Code/colo21-core/vendor/phpunit/phpunit/src/TextUI/Command.php(118): PHPUnit_TextUI_Command->run(Array, true)
13 /home/vagrant/Code/colo21-core/vendor/phpunit/phpunit/phpunit(52): PHPUnit_TextUI_Command::main()
14 {main}

Any help would be appreciated. Thanks.