FunSuite(個人非常推薦使用)

For teams coming from xUnit, FunSuite feels comfortable and familiar while still giving some of the benefits of BDD: 

FunSuite makes it easy to write descriptive test names, natural to write focused tests, 

and generates specification-like output that can facilitate communication among stakeholders.

import org.scalatest.FunSuite

class SetSuite extends FunSuite {

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

  test("Invoking head on an empty Set should produce NoSuchElementException") {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

FlatSpec

A good first step for teams wishing to move from xUnit to BDD, FlatSpec's structure is flat like xUnit, 

so simple and familiar, 

but the test names must be written in a specification style: "X should Y," "A must B," etc.

import org.scalatest.FlatSpec

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 {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

FunSpec

For teams coming from Ruby's RSpec tool, FunSpec will feel very familiar; More generally, for any team that prefers BDD, 

FunSpec's nesting and gentle guide to structuring text (with describe and it) 

provides an excellent general-purpose choice for writing specification-style tests.

import org.scalatest.FunSpec

class SetSpec extends FunSpec {

  describe("A Set") {
    describe("when empty") {
      it("should have size 0") {
        assert(Set.empty.size == 0)
      }

      it("should produce NoSuchElementException when head is invoked") {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

WordSpec

For teams coming from specs or specs2, WordSpec will feel familiar, and is often the most natural way to port specsN tests to ScalaTest. 

WordSpec is very prescriptive in how text must be written, so a good fit for teams who want a high degree of discipline enforced upon their

specification text.

import org.scalatest.WordSpec

class SetSpec extends WordSpec {

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

      "produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

FreeSpec

Because it gives absolute freedom (and no guidance) on how specification text should be written, 

FreeSpec is a good choice for teams experienced with BDD and able to agree on how to structure the specification text.

import org.scalatest.FreeSpec

class SetSpec extends FreeSpec {

  "A Set" - {
    "when empty" - {
      "should have size 0" in {
        assert(Set.empty.size == 0)
      }

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

PropSpec

PropSpec is perfect for teams that want to write tests exclusively in terms of property checks;

 also a good choice for writing the occasional test matrix when a different style trait is chosen as the main unit testing style.

import org.scalatest._
import prop._
import scala.collection.immutable._

class SetSpec extends PropSpec with TableDrivenPropertyChecks with Matchers {

  val examples =
    Table(
      "set",
      BitSet.empty,
      HashSet.empty[Int],
      TreeSet.empty[Int]
    )

  property("an empty Set should have size 0") {
    forAll(examples) { set =>
      set.size should be (0)
    }
  }

  property("invoking head on an empty set should produce NoSuchElementException") {
    forAll(examples) { set =>
       a [NoSuchElementException] should be thrownBy { set.head }
    }
  }
}

FeatureSpec

Trait FeatureSpec is primarily intended for acceptance testing, including facilitating the process of programmers working 

alongside non-programmers to define the acceptance requirements.

import org.scalatest._

class TVSet {
  private var on: Boolean = false
  def isOn: Boolean = on
  def pressPowerButton() {
    on = !on
  }
}

class TVSetSpec extends FeatureSpec with GivenWhenThen {

  info("As a TV set owner")
  info("I want to be able to turn the TV on and off")
  info("So I can watch TV when I want")
  info("And save energy when I'm not watching TV")

  feature("TV power button") {
    scenario("User presses power button when TV is off") {

      Given("a TV set that is switched off")
      val tv = new TVSet
      assert(!tv.isOn)

      When("the power button is pressed")
      tv.pressPowerButton()

      Then("the TV should switch on")
      assert(tv.isOn)
    }

    scenario("User presses power button when TV is on") {

      Given("a TV set that is switched on")
      val tv = new TVSet
      tv.pressPowerButton()
      assert(tv.isOn)

      When("the power button is pressed")
      tv.pressPowerButton()

      Then("the TV should switch off")
      assert(!tv.isOn)
    }
  }
}

RefSpec (JVM only)

RefSpec allows you to define tests as methods, which saves one function literal per test compared to style classes that represent tests as functions. 

Fewer function literals translates into faster compile times and fewer generated class files, which can help minimize build times. 

As a result, using Spec can be a good choice in large projects where build times are a concern as well as when 

generating large numbers of tests programatically via static code generators.

import org.scalatest.refspec.RefSpec

class SetSpec extends RefSpec {

  object `A Set` {
    object `when empty` {
      def `should have size 0` {
        assert(Set.empty.size == 0)
      }

      def `should produce NoSuchElementException when head is invoked` {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

Note: The "Ref" in RefSpec stands for reflection, which RefSpec uses to discover tests. As reflection is not availble in Scala.js, 

this class is not available on Scala.js.