How to create a test directory in Intellij 13?

You should have structure like this one:

 [] .idea    
 [] src
    [] main
      [] java   
           com.simpleproject
             SimpleClass.java
      [] resources
    [] test
      [] java
           com.simpleproject
             SimpleClassTest.java
      [] resources

After that go to: File->Project Structure->Modules and in "Sources" tab you can choose which folder is "test folder" (usually java in test), which "sources" (usually java in main) etc by clicking "Mark as" options.