Add open_below_at_eof() test

src/actions.rs

@@ -213,6 +213,14 @@ mod tests {
         assert_eq!(state.cursor.column, 0);
     }
 
+    #[test]
+    fn open_below_at_eof() {
+        let mut state = state("test\n");
+        state.cursor.line = 1;
+        open_below(&mut state);
+        assert_eq!(state.cursor.line, 1);
+    }
+
     #[test]
     fn move_line_up_preserve_column() {
         let mut state = state("test\n\ntest\n");