Configures and runs ScalaTest - Scala-native test framework with multiple specification styles (FlatSpec, FunSuite, WordSpec, FreeSpec, AsyncFlatSpec for async); Matchers DSL (`should equal`, `should contain`, `shouldBe a [Class]`); integrates with ScalaCheck for property-based testing; sbt + Maven + Gradle support; tagged-test selective execution. Use when working with Scala codebases.