Today I ancountered this problem when trying to run a test suite directly in the IDE. This happens when pressing right mouse button on the Spec class to get into the context menu.
update failed for AnAction with ID=RunClass: Failed to load class for test suite org.scalatest.FlatSpec
The option to run the test is not in the context menu any more. It happens on all ScalaTest suites in the project. JUnit test suites are ok.
My project compiles fine under both IDEA and SBT, and SBT can run all the tests without any problems.
Scala plugin 1.9.140