code: function expandVars(target, options) {
    const vars = options.vars || {};
    const regexp = /\$\{(\w+)\}/g;
  
    if (typeof target === "string") {
      return _expand(target);
    }
    for (let key in target) {
      target[key] = _expand(target[key]);
    }
    return target;
  
    function _expand(val) {
      let expanded = val;
      let match;
  
      while (match = regexp.exec(val)) {
        const varname = match[1];
        const varval = vars[varname] || process.env[varname];
        if (!varval) {
          debug(`could not expand variable \${${varname}}`);
          continue;
        }
        expanded = expanded.replace(`\${${varname}}`, varval);
      }
      return expanded;
    }
  }
docs: Expand variables, using variables from the `options` object,
  or process environment.
  Modifies the passed object in place.
  
  @private
  @param  {String|Object} target - object with parameters
  @param  {Object} options - test configurations
  @return {String|Object}