brief notes on mechanics of what's going on

modules/testing/src/test/scala/TestSyntaxExtensions.scala

@@ -23,14 +23,19 @@ class TestSyntaxExtensions
   test(
     "Arbitrary.oneOf produces values of each type, in plausible relative proportions."
   ) {
-    given Arbitrary[Boolean | Int] = Arbitrary.oneOf[Boolean, Int]
+    /* Establish the interval for plausible counts based on Normal approximation to the Binomial. */
     val n = 10000
     val (lowerBound, upperBound) =
       val zStar = 3.719016
       val p = 0.5
       val sd = scala.math.sqrt(n * p * p)
       val exp = n * p
       (-zStar * sd + exp, zStar * sd + exp)
+
+    // the instance under test
+    given Arbitrary[Boolean | Int] = Arbitrary.oneOf[Boolean, Int]
+
+    // Use the instance under test to generate the values, then count by type.
     forAll(Gen.listOfN(n, arbitrary[Boolean | Int])) { values =>
       val (bools, ints): (List[Boolean], List[Int]) =
         Alternative[List].separate(