Method expectsOuput not found on int when testing console commands in Lumen 5.8

Question

According to the Laravel documentation it looks like I should be able to chain methods to artisan commands in a unit test, like:

$this->artisan('make:docs')->expectsOutput('./openapi.yaml was generated.');

But in Lumen, $this->artisan returns an int so that doesn't work. This is the code from Lumen's Testing\TestCase.php:

 /**
 * Call artisan command and return code.
 *
 * @param string  $command
 * @param array   $parameters
 * @return int
 */
public function artisan($command, $parameters = [])
{
    return $this->code = $this->app['Illuminate\Contracts\Console\Kernel']->call($command, $parameters);
}

As a workaround I'm doing this, which isn't ideal since you have to add switches to bypass questions. This is a simple example with output only for questions I pass an array of switches to $this->execute using the $options parameter so I can skip them all and test the final output.

class CommandsTest extends TestCase
{
/**
 * Execute a console command.
 *
 * @param string $className
 * @param string $commandString
 * @param array $options
 *
 * @return CommandTester
 */
private function execute(string $className, string $commandString, array $options = []): CommandTester
{
    $application = new ConsoleApplication();

    $testedCommand = $this->app->make($className);
    $testedCommand->setLaravel(app());
    $application->add($testedCommand);

    $command = $application->find($commandString);

    $commandTester = new CommandTester($command);
    $commandTester->execute(array_merge(['command' => $command->getName()], $options));

    return $commandTester;
}

/**
 * Clean console command output.
 *
 * @param string $output
 *
 * @return string
 */
private function clean(string $output): string
{
    $output = trim($output);

    return str_replace(array("\r\n", "\r"), "\n", $output);
}

/**
 * Test the OpenAPI documentation command.
 *
 * @return void
 */
public function testMakeDocs(): void
{
    $command = $this->execute(DocsMake::class, 'make:docs');

    $output = $this->clean($command->getDisplay());

    $expected = './openapi.yaml was generated.';

    $this->assertSame($expected, $output);
}

Has anyone figured out how to make this work like Laravel so you can chain commands?