message: Refactor extract variable tests
  More consistent, readable and robust.
diff: @@ -27,6 +27,10 @@ class Selection {
  );
  }
  + static cursorAt(line: number, char: number): Selection {
  + return new Selection([line, char], [line, char]);
  + }
  +
  get start(): Position {
  return this._start;
  }
  