add boilerplate helper functions in persistent-vector-tests.sml to check if list contains indices that are in range, or are not in range

test/persistent-vector-tests.sml

@@ -1 +1,63 @@
-structure PersistentVectorTests = struct val tests = [] end
+structure PersistentVectorTests =
+struct
+  open Railroad
+  open Railroad.Test
+
+  fun isNotInRange (lst, pv) =
+    let
+      fun loopNotInRange lst =
+        case lst of
+          hd :: tl =>
+            if PersistentVector.isInRange (hd, pv) then
+              let
+                val msg =
+                  "idx " ^ Int.toString hd
+                  ^ " is in range when it shouldn't be\n"
+                val () = print msg
+              in
+                Expect.isTrue false
+              end
+            else
+              loopNotInRange tl
+        | [] => Expect.isTrue true
+    in
+      loopNotInRange lst
+    end
+
+  fun isInRange (lst, pv) =
+    let
+      fun loopInRange lst =
+        case lst of
+          hd :: tl =>
+            if PersistentVector.isInRange (hd, pv) then
+              loopInRange tl
+            else
+              let
+                val msg =
+                  "idx " ^ Int.toString hd
+                  ^ " is not in range when it should be\n"
+                val () = print msg
+              in
+                Expect.isTrue false
+              end
+        | [] => Expect.isTrue true
+    in
+      loopInRange lst
+    end
+
+  val initial =
+    let
+      val f = PersistentVector.append
+      val pv = PersistentVector.empty
+
+      val pv = f (1, 3, pv)
+      val pv = f (5, 7, pv)
+      val pv = f (9, 13, pv)
+      val pv = f (19, 27, pv)
+      val pv = f (33, 33, pv)
+    in
+      pv
+    end
+
+  val tests = []
+end