When you create a FlexUnit test case class for a Spark only Flex project and execute it, you get a compilation error.
Manually update the project component set to MX + Spark by following these steps:
Select the project for which you want to update the component set.
From the Flash Builder menu, select Project > Properties > Flex Build Path > Library Path.
Select the component set as MX + Spark.
Spark only project, compilation error, FlexUnit test, fails; cpsid_89948