But you will only need 1 VM :) For realistic testing of a multi-component stack, performance gains start adding up very quickly. There's also the start/teardown time if you want to run tests from a clean environment repeatedly.

In short: the right way to use VMs is as dumb chunks of hardware. Using them as logical units of software makes increasingly less sense as container-native tools get better.

(disclaimer: I'm the Docker guy :)