Suggestion

[Amin Raeisi]

More easier can be just add the follwing to your phpunit.xml file.
<env name="REDIS_CLIENT" value="mock"/>
Because then you can use redis when you are viewing your application (using homestead for example) and in testing it will be mocked as expected.

Thank for the package!

[Josias Montag]

Setting REDIES_CLIENT in .env.testing has the same effect, because phpunit.xml normally contains:
<env name="APP_ENV" value="testing"/>

Thanks for the hint though.