Annotation used to tag a test, or suite of tests, as being CPU-intensive (i.e., consuming a lot of CPU time when it runs).

Note: This is actually an annotation defined in Java, not a Scala trait. It must be defined in Java instead of Scala so it will be accessible at runtime. It has been inserted into Scaladoc by pretending it is a trait.

If you wish to mark an entire suite of tests as being CPU-intensive, you can annotate the test class with @CPU, like this:

package org.scalatest.examples.flatspec.cpuall

import org.scalatest._
import tags.CPU

@CPU
class SetSpec extends FlatSpec {

  "An empty Set" should "have size 0" in {
    assert(Set.empty.size === 0)
  }

  it should "produce NoSuchElementException when head is invoked" in {
    intercept[NoSuchElementException] {
      Set.empty.head
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the SetSpec in the above example with the @CPU tag annotation means that both tests in the class are CPU-intensive.

Another use case for @CPU is to mark test methods as CPU-intensive in traits Spec and fixture.Spec. Here's an example:

package org.scalatest.examples.spec.cpu

import org.scalatest._
import tags.CPU

class SetSpec extends RefSpec {

  @CPU def `an empty Set should have size 0` {
    assert(Set.empty.size === 0)
  }

  def `invoking head on an empty Set should produce NoSuchElementException` {
    intercept[NoSuchElementException] {
      Set.empty.head
    }
  }
}

The main use case of annotating a test or suite of tests is to select or deselect them during runs by supplying tags to include and/or exclude. For more information, see the relevant section in the documentation of object Runner.

Note that because reflection is not supported on Scala.js, this annotation will only work on the JVM, not on Scala.js.