In container testing answers the question: does my code work inside the container? Do I use the container's services correctly? Does the container work together with my the way I expect it to?
Out of container testing, on the other hand, has the advantage that you don't have to deploy before testing, and that the tests typically run considerably faster.
So you use out of container testing for faster feedback, in container testing for integration testing.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus