Remove functions.config.singleton

[saygun]

Description

functions.config() parses ENV variable(s) only once and saves the value into a variable for later usage. Thus setting a new value to process.env.CLOUD_RUNTIME_CONFIG is not causing getting a recent value.

Motivation
Calling the mockConfig function multiple times with different configuration values makes writing unit tests easier and gives flexibility to the developer. What do you think?

P.S This topic has been already mentioned in #68.

Code Sample

// spec/unit/auth-on-create.spec.ts
import test from 'firebase-functions-test';
const app = test();

describe('[Unit] Auth.onCreate()', () => {
  afterEach(() => {
    app.cleanup();
  });
  
  it('does something with config().foo', () => {
    app.mockConfig({ foo: 'bar' });
    ...
  });

  it('does something with config().baz', () => {
    app.mockConfig({ baz: 'qux' });
    ...
  });
});

[AlphonseSantoro]

This is exactly what I'm looking for. Is there anything blocking this?

[saygun]

Still waiting for the response from core members.

[saygun]

@laurenzlong @bkendall @ShoeBoom guys any comment on this?

[ShoeBoom]

I'm not actually a part of the firebase team btw. The code itself lgtm

[joehan]

LGTM - I'll release a new version of firebase-functions-test sometime later this week so y'all can use this. Thanks for the contribution!

[cwygoda]

Good evening y'all! Any chance to get this released?