PubSub already loaded console warning

[adamstankiewicz]

In @edx/frontend-platform, running the tests, there are many console warnings about "PubSub already loaded, using existing version". These console warnings can also be seen in some MFE test suites, as well.

PASS src/initialize.test.js
  ● Console
    console.warn
      PubSub already loaded, using existing version
      18 |  */
      19 |
    > 20 | import PubSub from 'pubsub-js';
         | ^
      21 |
      22 | /**
      23 |  *
      at node_modules/pubsub-js/src/pubsub.js:15:17
      at Object.<anonymous> (node_modules/pubsub-js/src/pubsub.js:35:2)
      at Object.<anonymous> (src/pubSub.js:20:1)
PASS src/analytics/interface.test.js

AC

• Identify what's causing the console warnings about PubSub already being loaded.
• Fix so that there are no more console warnings about PubSub already being loaded.

[ishahroz]

When running the test cases, these console warnings come as a result of the singleton pattern being used in the PubSub package. According to this PR, it gives information on if PubSub is already initialised on the root level, that root instance should be used instead of overriding with an empty new one.

After doing root cause analysis, I could pull some of the following observations:

1. These console warnings only come when running the following test suites in @edx/frontend-platform:

• src/initialize.test.js
• src/react/AuthenticatedPageRoute.test

2. In both these test suites, we find common auth interface being imported src/auth/interface.js, and which indirectly imports and employs PubSub module.

3. After removing PubSub wrapper import (import { publish } from '../pubSub') from src/auth/interface.js, we no longer get to see these console warnings.

4. But removing so, it will create ripple since we are using publish method in some of src/auth/interface.js methods. So, to incorporate the removed lines, I wrote their implementation in src/auth/MockAuthService.js but in turn, we get to see the same console warnings after running the test cases.

Moreover, these console warnings merely provide information to reinforce singleton use of PubSub. Maybe instead of passing this information as console warning, it should be documented or set lower message priority level.