Mockery's andReturn() executing method instead of mocking return value

I'm Trying to test the following method:

/* ConfigurationService.php*/    

public function checkConfigs()
{
    $configurations = $this->getConfigurations();
    return $configurations['configExample'] === '1';
}

Considering that the getConfigurations() method calls other methods outside this file, inside ConfigurationRepository.php, I've tried to mock only its return and execute the method that I wanna test(checkConfigs()): (some code ommited)

/* ConfigurationServiceTest.php */       

$configurationRepoMock = \Mockery::mock(ConfigurationRepository::class);
$configurationRepoMock
    ->shouldReceive('getConfigurations')
    ->once()
    ->andReturn(['configExample' => '1']);

$configurationServiceMock = \Mockery::mock(ConfigurationService::class);
$this->app->instance('App\Services\ConfigurationService', $configurationServiceMock);

$configurationServiceInstance = new ConfigurationService($configurationRepoMock);
$response = $configService->checkConfigs();

---

The PROBLEM is, instead of returning the mocked result(['configExample' => '1']), the method getConfigurations() executes, failing due to other method calls inside of it, returning the error:

Mockery\Exception\BadMethodCallException: Received Mockery_1_App_Repositories_API_ConfigurationRepository::methodInsideGetConfigurations(), but no expectations were specified

Summing up, andReturn() is not working. Any ideas?