text: 'use strict';
  
  var assert = require('assert');
  
  module.exports = function (filepath, contents, stat) {
    assert(
      typeof contents === 'string' || contents instanceof Buffer,
      'Expected `contents` to be a String or a Buffer'
    );
  
    var file = this.store.get(filepath);
    file.isNew = file.contents === null;
    file.state = 'modified';
    file.contents = typeof contents === 'string' ? Buffer.from(contents) : contents;
    file.stat = stat;
    this.store.add(file);
  
    return file.contents.toString();
  };
  