text: void test_lookup_returns_dynamic_binding() {
    cell* var = new_sym("a");
    cell* val = new_num(34);
    new_dynamic_scope(var, val);
      CHECK_EQ(lookup(var), val);
    end_dynamic_scope(var);
  }
  
  void test_new_dynamic_scope_increments_refcounts() {
    cell* var = new_sym("a");
    cell* val = new_num(34);
    CLEAR_TRACE;
    new_dynamic_scope(var, val);
      CHECK_EQ(excess_mkrefs(), 2);   // one for var, one for val
    end_dynamic_scope(var);
  }
  