firefly-iii/app/tests/TestCase.php

<?php

class TestCase extends Illuminate\Foundation\Testing\TestCase
{

    /**
     * Creates the application.
     *
     * @return \Symfony\Component\HttpKernel\HttpKernelInterface
     */
    public function createApplication()
    {
        $unitTesting = true;

        $testEnvironment = 'testing';

        return require __DIR__ . '/../../bootstrap/start.php';
    }

    public function mock($class)
    {
        $mock = Mockery::mock($class);

        $this->app->instance($class, $mock);

        return $mock;
    }

}