add todos enzyme tests

[mwilc0x]

This PR adds enzyme tests for the todos example components

This is part of #1481

[gaearon]

I specifically didn’t mention todos in #1481 because @jontewks was already working on it in #1471. I should have communicated this better 😥 .

Ultimately we want to use enzyme in all our tests so this probably supersedes @jontewks’s work. I apologize for not handling it better.

Can you please make sure that this includes whatever tests existed in #1471?

[mwilc0x]

Yeah this was my fault, I should have checked the open PR's first. I reviewed #1471 and it looks like this includes all the tests from there.

[whoisandy]

Aren't the component tests for todo-with-undo the same as todos? Trying to figure out if there's any other component test that has to be added. The action and reducer tests are missing though. Since redux-undo is already tested, minor tweaks in action and reducer tests might be sufficient.

[gaearon]

Shouldn’t we be able to get rid of jsdom now?

[mwilc0x]

Yeah, we can safely remove jsdom now. Good catch, thanks. I've updated the PR with 0baa696 to reflect this.

[timdorr]

Can this be reworked to also remove/replace the existing React Test Utils tests?

[mwilc0x]

@timdorr sure, we can do that. If anyone else is interested, please feel free to chime in. I wouldn't be able to start these until tomorrow.

[mwilc0x]

@timdorr I started by converting one file, does this look ok to you?

[timdorr]

Thanks for the efforts @mjw56. We're going to go down the route of using react-test-renderer instead.