begin adding normal-delete tests

test/normal-delete.sml

@@ -1,2 +1,59 @@
 structure NormalDelete =
-struct open Railroad open Railroad.Test open InputMsg val tests = [] end
+struct
+  open Railroad
+  open Railroad.Test
+  open InputMsg
+
+  val dhDelete = describe "delete motion 'dh'"
+    [ test "does not delete when cursor is at index 0" (fn _ =>
+        let
+          (* arrange *)
+          val originalString = "hello world\n"
+          val app = TestUtils.init originalString
+          val app = AppWith.idx (app, 0)
+
+          (* act *)
+          val app = TestUtils.updateMany (app, "dh")
+
+          (* assert *)
+          val expectedString = originalString
+          val actualString = LineGap.toString (#buffer app)
+        in
+          Expect.isTrue (expectedString = actualString)
+        end)
+    , test "does not delete when character before cursor is a newline" (fn _ =>
+        let
+          (* arrange *)
+          val originalString = "hello\nworld\n"
+          val app = TestUtils.init originalString
+          val app = AppWith.idx (app, 6)
+
+          (* act *)
+          val app = TestUtils.updateMany (app, "dh")
+
+          (* assert *)
+          val expectedString = originalString
+          val actualString = LineGap.toString (#buffer app)
+        in
+          Expect.isTrue (expectedString = actualString)
+        end)
+    , test "deletes one char to the left when on a non-newline" (fn _ =>
+        let
+          (* arrange *)
+          val originalString = "hello world\n"
+          val app = TestUtils.init originalString
+          val app = AppWith.idx (app, 5)
+
+          (* act *)
+          val app = TestUtils.updateMany (app, "dh")
+
+          (* assert *)
+          val expectedString = "hell world\n"
+          val actualString = LineGap.toString (#buffer app)
+        in
+          Expect.isTrue (expectedString = actualString)
+        end)
+    ]
+
+  val tests = [dhDelete]
+end