In ScalaTest 2.1.0, String beauty is no longer just skin deep

gistfile1.scala

// In ScalaTest/ScalaUtils 2.1.0 the Prettifier, which in 2.0 just prettified objects at the top level,
// has been enhanced to prettify objects contained inside other objects, including Scala and Java
// collections, Option, Either, and Try. Here's an example:

scala> val actual = Set(List(Map(1 -> Some("2"), 2 -> Some("3"))))
actual: scala.collection.immutable.Set[List[scala.collection.immutable.Map[Int,Some[String]]]] =
    Set(List(Map(1 -> Some(2), 2 -> Some(3))))

scala> val expected = Set(List(Map('1' -> Some(2), '2' -> Some(3))))
expected: scala.collection.immutable.Set[List[scala.collection.immutable.Map[Char,Some[Int]]]] =
    Set(List(Map(1 -> Some(2), 2 -> Some(3))))

// Note that the toStrings above are identical with each other, even though none
// of the types are identical. Now take a look at an error message involving these
// values:

scala> import org.scalatest.Assertions._
import org.scalatest.Assertions._

scala> assert(actual == expected)
org.scalatest.exceptions.TestFailedException: Set(List(Map(1 -> Some("2"), 2 -> Some("3")))) did not
    equal Set(List(Map('1' -> Some(2), '2' -> Some(3))))

// ScalaTest 2.1.0 prettified the Strings that were inside an Option that were values in a Map contained
// inside a List sitting inside a first Set, and prettified the Chars that were keys in the Map in the
// List in the second Set.

// Of course a better way to detect this particular kind of problem is at compile time. Since the two
// types of expected and actual are different, you could catch the bug this way:

scala> import org.scalautils.TypeCheckedTripleEquals._
import org.scalautils.TypeCheckedTripleEquals._

scala> assert(actual === expected)
<console>:28: error: types scala.collection.immutable.Set[List[scala.collection.immutable.Map[Int,Some[String]]]]
    and scala.collection.immutable.Set[List[scala.collection.immutable.Map[Char,Some[Int]]]] do not adhere to the
    type constraint selected for the === and !== operators; the missing implicit parameter is of type
    org.scalautils.Constraint[scala.collection.immutable.Set[List[scala.collection.immutable.Map[Int,Some[String]]]],
    scala.collection.immutable.Set[List[scala.collection.immutable.Map[Char,Some[Int]]]]]
              assert(actual === expected)
                            ^

// The rather long-winded compiler error message explains that the types are not compatible for being compared
// for equality. Nevertheless, many error messages do make it out the door as test failures, and
// the enhanced Prettifier in 2.1.0 should help clarify which objects were involved.