Test server not returning workflow results

Running the example test (mocking activities) described in the official temporal docs and here results in a hanging test, since getResults() does not return, example:-

$run = $this->workflowClient->start($workflow, 'world');
$result = $run->getResult();

I have reproduced the issue by forking the sample-php repo and adding a test as per above docs.

To run example:-

git clone https://github.com/stock2shop/samples-php.git
cd samples-php/app/
git checkout tests
cd app
composer install
./vendor/bin/rr get-binary
php vendor/bin/phpunit

You will notice the test does not complete.
When debugging you will see it hangs on getResults().

I am sure there is some config I am missing between rr and the test server…
If someone has any advice that would be greatly appreciated.

It seems like my test worker was missing num_workers:

temporal:
  activities:
    num_workers: 10

Seems to be working now.