scala - "Unknown artifact. Not resolved or indexed" error for scalatest

Question

I'm trying to modify the build.sbt file to add scalatest dependencies in IntelliJ IDEA. There's no error log in the console but I got a Unknown artifact. Not resolved or indexed. when I hovered my mouse over the underline. How do I solve this? Many thanks in advance!

This is the line I used to add dependency: libraryDependencies += "org.scalatest" % "scalatest_2.11" % "3.0.1" % "test"

And here is what my screen looks like:

Answer 1

If you just added the dependency, it might not have been downloaded yet. Refresh/reimport the project to do so.

If it has already been downloaded, press Alt+Enter in IntelliJ on the lines with the warning and select the "update project resolvers' indexes" quickfix, then select the "local cache" index and click "update".

You can verify that the update worked by checking the date in the "Updated" column: