begin adding tests for persistent-vector.sml, and add bug fix to 'PersistentVector.delete' in light of one of the tests. (We were decrementing by the wrong value previously, but I fixed it and added a comment of how we arrive at the value we want to decrement by

test/persistent-vector-tests.sml

@@ -0,0 +1,55 @@
+structure PersistentVectorTests =
+struct
+  open Railroad
+  open Railroad.Test
+
+  structure Pv = PersistentVector
+
+  val appendTests = describe "PersistentVector.append"
+    [test "appends new values to end" (fn _ =>
+       let
+         (* arrange *)
+         val pv = Pv.fromList [(1, 1), (3, 3)]
+
+         (* act *)
+         val pv = Pv.append (5, 7, pv)
+
+         (* assert *)
+         val outputList = Pv.toList pv
+         val expectedList = [(1, 1), (3, 3), (5, 7)]
+       in
+         Expect.isTrue (outputList = expectedList)
+       end)]
+
+  fun printList lst =
+    let
+      val str =
+        List.map
+          (fn (start, finish) =>
+             "(" ^ Int.toString start ^ ", " ^ Int.toString finish ^ ")") lst
+      val str = "[" ^ String.concatWith ", " str ^ "]\n"
+    in
+      print str
+    end
+
+  val deleteTests = describe "PersistentVector.delete"
+    [test
+       "deletes last value correctly \
+       \when only last value is in deletion range"
+       (fn _ =>
+          let
+            (* arrange *)
+            val pv = Pv.fromList [(0, 0), (3, 3), (5, 5)]
+
+            (* act *)
+            val pv = Pv.delete (5, 1, pv)
+
+            (* assert *)
+            val outputList = Pv.toList pv
+            val expectedList = [(0, 0), (3, 3)]
+          in
+            Expect.isTrue (outputList = expectedList)
+          end)]
+
+  val tests = [appendTests, deleteTests]
+end

test/test.sml

@@ -5,13 +5,13 @@ struct
 
   fun main () =
     let
-      val tests =
-        List.concat
-          [ NormalMove.tests
-          , NormalDelete.tests
-          , Regression.tests
-          , RegexTests.tests
-          ]
+      val tests = List.concat
+        [ NormalMove.tests
+        , NormalDelete.tests
+        , Regression.tests
+        , RegexTests.tests
+        , PersistentVectorTests.tests
+        ]
       val tests = concat tests
     in
       runWithConfig [Configuration.PrintPassed false] tests