Examples: add tests

[fryorcraken]

non-regression tests are needed to ensure that the show case, deployed on master branch updates, still works.

Also, remove WakuMock once the tests are in place.

[fryorcraken]

Adding remove some agility to examples. As when a hacker play with them they may need to update/remove the tests.

Could do very basic tests:

• check components are rendered/usable
• Check no errors in logs

Best to ship first with the new react components.
Code readability is most important.

In terms of testing usefulness for examples. Hopefully, any functional issue with Waku would be detected in the js-waku test suite.
What could happen is the fact that the example does not use a Waku API correctly or hit a corner case which would lead to an error so the detection of error in logs would be a great start/low hanging fruit.

[weboko]

In waku-org/js-waku#1542 this was partially addressed.
Other things will be completed in waku-org/js-waku#1597

I think at this point this issue can be closed.

@fryorcraken re-open if disagree