We have deleted the lib/quasar.jar and updated the docs to change the way we recommend running tests inside IntelliJ. It's a bit controversial, but we did this for the following reasons:
when corda 4 was released, everyone forgot to update the quasar.jar in the template projects to the corda 4 version
customers who had written cordapps based on the template needed to know to update the quasar version in their existing cordapps, but this was missed from the upgrade nodes
we could have written some gradle to automatically download the jar file, but you still have to do the -javaagent dance each time you run a new test
So because of this we picked recommending running using the gradle test runner. This means you run tests the same way that the build does, which is good, and we can leverage the quasar-utils plugin. It also means you can run any test and it just works. I've tested debugging and it feels the same as using the JUnit runner.