If you remove it, will cause such a result:  `mvn dependency:tree`
 
	[INFO] +- org.scalatest:scalatest_2.10:jar:1.9.1:test
	[INFO] |  +- org.scala-lang:scala-actors:jar:2.10.0:test
	[INFO] |  \- org.scala-lang:scala-reflect:jar:2.10.3:test