[feature] adds spy.calledImmediatelyBefore and spy.calledImmediatelyAfter

[timcosta]

Purpose (TL;DR) - mandatory

Sometimes you need to be sure that you are calling a().c() and not a().b().c(). When mocking a large library like knexjs, being able to ensure the exact order of calls is incredibly helpful.

Background (Problem in detail) - optional

When mocking a large library that chains calls, you may end up writing one large mock in the beforeEach of the test library as to not duplicate code within your tests. Unfortunately there is no way to ensure that chained calls do not sneak into calls chains currently, as the calledBefore and calledAfter implementations simply use > or <. In order to use a large mock and reduce duplicitous code in test suites when dealing with libraries that chain calls, calledImmediatelyBefore and calledImmediatelyAfter allow you to ensure that no additional modifiers end up between your chained calls.

Solution - optional

This solution works just like calledBefore and calledAfter, but uses strict equality to ensure that the calls to the spies did in fact happen sequentially.

How to verify - mandatory

1. Check out this branch (see github instructions below)
2. npm install
3. npm test (includes 100% test coverage)

[coveralls]

Coverage increased (+0.03%) to 95.372% when pulling 3aa9919 on timcosta:add_called_immediately_before_after into e401337 on sinonjs:master.

[mroderick]

Thank you for the pull request. I only have a couple of comments

[mroderick]

This is minor, but it would make the tests easier to read, if you use A in both description and implementation. Otherwise readers would have to understand that A is this.spy1

[mroderick]

Same here, A is this.test1

[timcosta]

Thanks for reviewing @mroderick - updated the names in my tests and the tests i stole the template from.

[coveralls]

Coverage increased (+0.03%) to 95.372% when pulling a957ef3 on timcosta:add_called_immediately_before_after into e401337 on sinonjs:master.