Question

I am trying to write a bunch of test codes against a Java class library and I am using specs2 on Scala.

I have a group of test cases that should be ran for all the subclasses of class T,
but could not figure out the best way to implement this.

Coming from Ruby, I naturally sought something like *shared_examples_for* macro as in Rspec, but there seems to be no such thing in specs2.

Then I thought, subclassing my own Specification subclass with test cases may be one way to go.

Is there any tidier solution to this?

Answer 1

You can find an example of shared examples in the User Guide. Basically this uses the fact that you can define a method taking a specific instance to test and declare examples for it (see the nonEmptyStack method).

If this helps let me kickstart you with a quick example using a mutable Specification:

 import org.specs2._

 class SubclassesSpec extends mutable.Specification {
   "These examples must pass for all subclasses" >> {
     subclasses foreach { subclass => examples(subclass) }
   }

   /** @return instances of subclasses of type T where T is 
    * the supertype of the classes you want to test */
   def subclasses: Seq[T] = ...

   /** @return examples parameterized by a specific instance */
   def examples(t: T) = {
     "this is the first example" >> {
       // use t here
     }
     "this is the second example" >> {
       // use t here
     }
   }
 }

The only thing you need to check before you do that is the possible side-effects between examples. In the specification above, all the examples are executed concurrently and they share the same object. If that creates any issue, you can either:

• add sequential at the top of the specification to avoid concurrency

• change subclasses and examples to def subclasses: Seq[() => T] and def examples(t: () => T) so that you will create a brand new instance for each example