Use Nimble for test matchers

[czechboy0]

Let's modernize & simplify our tests with https://github.com/Quick/Nimble

[cojoj]

In that case it'd be advisable to change the whole testing approach to BDD and use both Quick and Nimble... I don't know if they support code coverage?

[cojoj]

And one more thing from me...
If we're going to rewrite test cases we should fix some issues at the same time, so we don't speed up and leave some tech debt. I mean, we have:

• Re-record test cassettes with Xcode 7 Beta 6 changes #98
• Change API call signatures to use ErrorType instead of NSError #81
• Add missing functionalities to support API #40 (one last tiny piece of feature... 🙏)

[czechboy0]

Actually I don't want to use Quick. I want to keep using vanilla XCTest so that we can still run separate tests one by one etc. I just want to use Nimble matchers instead of XCTestAssertEqual.... Using all the way up to Quick takes away too many good Xcode and XCTest features for my taste.

Agreed that we should fix those issues as well, but let's take it one step at a time.

[cojoj]

Makes sense 👍