在Mocha中编写Meteor Blaze渲染测试时遇函数不存在错误求助

That error pops up because your Blaze template is trying to call a function named _ that isn’t available in your Mocha test environment. The _ function is most commonly either Underscore/Lodash (used for utility operations) or an i18n helper (like from tap:i18n for translations). Let’s break down how to fix both scenarios:

If you’re using _ for Underscore/Lodash #

Meteor includes Underscore by default, but sometimes in test mode, the global _ isn’t exposed properly. Here are two quick fixes:

1. Explicitly import Underscore in your test file
   Add this at the top of your test script to make _ available globally for the template to access:

   import _ from 'underscore';
   global._ = _;
   

2. Pass _ directly to the template context
   When rendering the template in your test, include _ in the data object to avoid relying on globals:

   const template = Blaze.renderWithData(Template.yourTemplate, { _: _ }, document.body);
   

If you’re using _ as an i18n helper (e.g., tap:i18n) #

If your template uses {{_ 'translation-key'}} for internationalization, the helper isn’t registered in your test setup. Try these solutions:

1. Load the i18n package in tests
   Ensure your test command includes all necessary packages. If you’re using meteor test, it should load tap:i18n automatically, but double-check with meteor list to confirm the package is installed.

2. Mock the i18n helper
   If you don’t want to spin up the full i18n system for tests, register a mock helper before rendering:

   beforeEach(() => {
     Template.registerHelper('_', (key) => {
       return key; // Return the key itself, or a custom mock translation
     });
   });
   

   This lets your template render without throwing errors, and you can assert against the mock output.

Quick Troubleshooting Tip #

First, check your template code to see exactly how _ is being used. If it’s in a loop like {{#each _.keys(items)}}, it’s Underscore. If it’s {{_ 'welcome-message'}}, it’s almost certainly an i18n helper. Knowing which one you’re dealing with will save you time!

Example Test Setup for Underscore #

import { Blaze } from 'meteor/blaze';
import { Template } from 'meteor/templating';
import _ from 'underscore';
import './yourTemplate.html';

describe('Your Template', () => {
  let testDiv;

  beforeEach(() => {
    testDiv = document.createElement('div');
    global._ = _; // Make Underscore available globally
  });

  afterEach(() => {
    Blaze.remove(testDiv);
  });

  it('renders without errors', () => {
    Blaze.renderWithData(Template.yourTemplate, { items: { a: 1, b: 2 } }, testDiv);
    // Add your assertions here, e.g., check if items are rendered correctly
  });
});

内容的提问来源于stack exchange，提问作者Saransh Dev Singh