如何在ScalaTest中使用ScriptEngine

以下测试应该通过,但事实并非如此

class EngineTest extends FunSuite {

  test("engine should not be null") {
    val manager: ScriptEngineManager = new ScriptEngineManager
    val engine: ScriptEngine = manager.getEngineByName("nashorn")
    assert(engine != null)
  }
}

在manager.getEngineFactories()似乎是空的.为什么？如何初始化上下文？