add tests to verify that cursorIdx is as expected after 'dh' delete motion

test/normal-delete.sml

@@ -53,6 +53,66 @@ struct
         in
           Expect.isTrue (expectedString = actualString)
         end)
+    , test "moves cursor left by one after deleting left char" (fn _ =>
+        let
+          (* arrange *)
+          val originalIdx = 5
+          val originalString = "hello world\n"
+
+          val app = TestUtils.init originalString
+          val app = AppWith.idx (app, originalIdx)
+
+          (* act *)
+          val {cursorIdx, ...} = TestUtils.updateMany (app, "dh")
+        in
+          (* assert *)
+          Expect.isTrue (cursorIdx = originalIdx - 1)
+        end)
+    , test "deletes 3 chars and moves cursor left by 3 when count is 3" (fn _ =>
+        let
+          (* arrange *)
+          val originalIdx = 5
+          val originalString = "hello world\n"
+
+          val app = TestUtils.init originalString
+          val app = AppWith.idx (app, originalIdx)
+
+          (* act *)
+          val {cursorIdx, buffer, ...} = TestUtils.updateMany (app, "3dh")
+
+          (* assert *)
+          val expectedString = "he world\n"
+          val deleted3CharsInString = expectedString = LineGap.toString buffer
+          val cursorIdxIsDecrementedBy3 = cursorIdx = originalIdx - 3
+        in
+          Expect.isTrue
+            (cursorIdxIsDecrementedBy3 andalso deleted3CharsInString)
+        end)
+    , test
+        "deletes until start column when \
+        \count is greater than current column"
+        (fn _ =>
+           let
+             (* arrange *)
+             val originalIdx = 5
+             val originalString = "hello world\n"
+
+             val app = TestUtils.init originalString
+             val app = AppWith.idx (app, originalIdx)
+
+             (* act *)
+             val {cursorIdx, buffer, ...} = TestUtils.updateMany (app, "9dh")
+
+             (* assert *)
+             val actualString = LineGap.toString buffer
+             val expectedString = " world\n"
+             val stringIsExpected = actualString = expectedString
+
+             val expectedCursorIdx = 0
+             val cursorIdxIsExpected = cursorIdx = expectedCursorIdx
+           in
+             Expect.isTrue (stringIsExpected andalso cursorIdxIsExpected)
+           end)
     ]
 
   val tests = [dhDelete]