Diff for hasProperties

[alexbepple]

When using hasProperties we are more interested in the given properties than in anything else. So the diff becomes more useful if only the differing aspects are shown. describeMismatch uses a similar reasoning.

In order to do this, I had to change the diff API. Cp. #7 (comment)
I refactored the early beginnings that we had so far.

When creating the diff objects in hasProperties, I considered the following situations:

• direct properties (implicit equalTo)
• diff-capable matcher
• non-diff-capable matcher
• multiple nesting, e.g. __.hasProperties({a: __.hasProperties({b: __.greaterThan(2)})})

Real-life example

Before

After

(with a custom property matcher for nicer formatting)

[rluba]

Hi Alex,

thank you for the pull request and sorry for the delay.

Looks great, but I think your hasProperties.getDiffItems breaks if hasProperties is a promising matcher due to promising sub-matchers. Retaining promise-awareness can be quite tricky, event when using promiseAgnostic.

Do you think you can update the PR accordingly?

Although I doubt that anyone already uses the diff API for custom matchers, I will nonetheless increase the major version when merging due to the breaking API changes.