scalatest - install and use scalatest with eclipse

The site to install update from Eclips is 

URL: http:///download.scala-ide.org/sdk/e37/scala29/stable/site

and as of how to run the Test within the Scala IDE you can :

For Eclipse users, ScalaTest offers a powerful plugin that provides seamless support for testing in the Scala IDE for Eclipse. Not only does this plugin give Scala programmers the level of test-framework/IDE integration that Java programmers have enjoyed with JUnit, it goes quite a bit farther:

1. You can right click on any test or collection of tests and run them.
2. You can run just the tests you select in code, run tests you select in reported results, rerun all tests or just previously failed tests, or run tests in a selected class, file, or package.
3. The results pane mirrors the structure or the specification (i.e., if your BDD-style specification text is nested in the source, it will appear nested in the results pane).
4. You can hop from results to test, scope, class, or line of failed code.
5. You can unfold the top of that stack that is automatically folded so only the offending line of code is shown.
6. And, because ScalaTest is a platform that can support different styles of testing, the plugin can be extended to grant full IDE support for non-ScalaTest-native styles, such as a ScalaCheck Properties classes, Specs2 Specifications, or custom styles.

or 

Reference: 

Using Scala Test with Eclipse