Add backspace_start_of_buffer unit test

src/actions.rs

@@ -230,6 +230,14 @@ mod tests {
         delete_char_backward(&mut state);
     }
 
+    #[test]
+    fn backspace_start_of_buffer() {
+        let mut state = state("test\n");
+        let original = state.buffer.as_ref().clone();
+        delete_char_backward(&mut state);
+        assert_eq!(original, *state.buffer.as_ref());
+    }
+
     #[test]
     fn append_on_newline() {
         let mut state = state("test\ntest\n");