add failing test for 'dj' motion, and progress reimplementing 'MakeNormalDelete.deleteLine'

fcore/normal-mode/make-normal-delete.sml

@@ -361,14 +361,17 @@ struct
         else endLineIdx
       val buffer = LineGap.goToIdx (endLineIdx, buffer)
     in
-      if Cursor.isOnNewlineAfterChr (buffer, endLineIdx) then
+      if Cursor.isCursorAtStartOfLine (buffer, endLineIdx) then
         let
-          val endLineIdx = endLineIdx + 1
+          val endLineIdx =
+            if endLineIdx = #textLength buffer - 1 then endLineIdx - 1
+            else endLineIdx + 1
 
           val length = endLineIdx - startIdx
           val initialMsg = Fn.initMsgs (startIdx, length, buffer)
           val buffer = LineGap.delete (startIdx, length, buffer)
 
+          (* just need to reposition the cursor *)
           val ss = LineGap.toString buffer
           val ss = String.toCString ss ^ "\n"
           val () = print ss

test/normal-delete.sml

@@ -436,6 +436,28 @@ struct
            in
              Expect.isTrue (stringIsExpected andalso cursorIdxIsExpected)
            end)
+    , test "deletes two lines when cursor is on a newline" (fn _ =>
+        let
+          (* arrange *)
+          val originalString = "\nhello\nworld\ntrello\brillo\n"
+          val originalIdx = 0
+
+          val app = TestUtils.init originalString
+          val app = AppWith.idx (app, originalIdx)
+
+          (* act *)
+          val {cursorIdx, buffer, ...} = TestUtils.updateMany (app, "dj")
+
+          (* assert *)
+          val expectedString = "world\ntrello\nbrillo\n"
+          val actualString = LineGap.toString buffer
+          val stringIsExpected = expectedString = actualString
+
+          val expectedCursorIdx = 0
+          val cursorIdxIsExpected = expectedCursorIdx = cursorIdx
+        in
+          Expect.isTrue (stringIsExpected andalso cursorIdxIsExpected)
+        end)
     ]
 
   val tests = [dhDelete, dlDelete, djDelete]