While setting up unit testing for a PHP project, I ran into this error when I first tried to run the simple example tests to prove the system was set up correctly:
RuntimeException: The only supported ciphers are AES-128-CBC and AES-256-CBC with the correct key lengths.
Searching for this error revealed that, by far, this issue most commonly happened when you had an improper app key, and the solution was simply to regenerate the key — but this was not my problem, because I had a perfectly valid app key. I even regenerated it for good measure, and still I got the error. Nothing else on the first two pages of Google provided any help for my situation, and once I started getting the foreign-language pages I knew I was on my own.
Fortunately, in this case, the solution proved to be simple. In the phpunit.xml file Laravel automatically generates, I found this in the section for setting up environment variables:
<env name="APP_ENV" value="testing"/>
Aha! It was set to look for the testing environment, aka .env.testing! Sure enough, my environment file had the application key set to, literally, the word “key”. I simply copied over my main .env file into .env.testing, ensuring the correct key value was provided, and this solved the issue.