import scalatest shows unresolved even after dumping maven dependency in intellij

Question

I am using intellij 2018 . I have dumped scalatest libraries through build.sbt and I could see libraries in external dependencies in project.

libraryDependencies += "org.scalatest" %% "scalatest" % "3.3.0-SNAP2" % Test

But when I import scalatest library in class it is showing not resolved.

how to make this work ?

import org.scalatest.flatspec.AnyflatSpec