Comparing collection contents with ScalaTest

问题:

I'm trying to unit-test some Scala that is very collection-heavy. These collections are returned as Iterable[T], so I am interested in the contents of the collection, even if the underlying types differ. This is actually two related problems:

1. How do I assert that two ordered collections contain the same sequence of elements?
2. How do I assert that two unordered collections contain the same set of elements?

In summary, I'm looking the Scala-equivalent of NUnit's CollectionAssert.AreEqual (ordered) and CollectionAssert.AreEquivalent (unordered) in ScalaTest:

Set(1, 2) should equal (List(1, 2))          // ordered, pass
Iterable(2, 1) should equal (Iterable(1, 2)) // unordered, pass

回答1:

You could try .toSeq for ordered collections and .toSet for unordered, which captures what you want as far as I understand it.

The following passes:

class Temp extends FunSuite with ShouldMatchers {
  test("1")  { Array(1, 2).toSeq should equal (List(1, 2).toSeq) }
  test("2")  { Array(2, 1).toSeq should not equal (List(1, 2).toSeq) }
  test("2b") { Array(2, 1) should not equal (List(1, 2)) }  
  test("3")  { Iterable(2, 1).toSet should equal (Iterable(1, 2).toSet) }
  test("4")  { Iterable(2, 1) should not equal (Iterable(1, 2)) }
}

BTW a Set is not ordered.

edit: To avoid removing duplicate elements, try toSeq.sorted. The following pass:

  test("5")  { Iterable(2, 1).toSeq.sorted should equal (Iterable(1, 2).toSeq.sorted) }
  test("6")  { Iterable(2, 1).toSeq should not equal (Iterable(1, 2).toSeq) }

edit 2: For unordered collections where elements cannot be sorted, you can use this method:

  def sameAs[A](c: Traversable[A], d: Traversable[A]): Boolean = 
    if (c.isEmpty) d.isEmpty
    else {
      val (e, f) = d span (c.head !=)
      if (f.isEmpty) false else sameAs(c.tail, e ++ f.tail)
    }

e.g. (note use of symbols 'a 'b 'c which have no defined ordering)

  test("7")  { assert( sameAs(Iterable(2, 1),    Iterable(1, 2)     )) }
  test("8")  { assert( sameAs(Array('a, 'c, 'b), List('c, 'a, 'b)   )) }
  test("9")  { assert( sameAs("cba",             Set('a', 'b', 'c') )) }

---

Alternative sameAs implementation:

  def sameAs[A](c: Traversable[A], d: Traversable[A]) = {
    def counts(e: Traversable[A]) = e groupBy identity mapValues (_.size)
    counts(c) == counts(d)
  }

回答2:

Meanwhile you can use

Iterable(2, 1) should contain theSameElementsAs Iterable(1, 2)

To test the ordered set you have to convert it to a sequence.

Set(1, 2).toSeq should contain theSameElementsInOrderAs List(1, 2)