Render diffs for expected / actual test results

[xiongtx]

Renders diffs provided by clojure-emacs/cider-nrepl#478 in test result buffer.

(deftest my-test
  (is (= {:a 1 :b 2}
         {:a 2 :b 3}
         {:c "a" :d "b"})))

[bbatsov]

Looks pretty cool!

Just two notes from me:

• How is this going to look for big data structures?
• Did you know about the ediff support in cider-test? :-)

This change also requires a changelog entry.

[xiongtx]

• How is this going to look for big data structures?'

Arguably better than currently:

1. Forms are now inserted via insert-rectangle, so they align properly
2. actual values are displayed individually (w/ diffs below) instead of in a single (not (= ...))

Did you know about the ediff support in cider-test? :-)

I was vaguely aware of it, but Ediff:

1. Is heavy-handed

• Changes your window configuration or creates a new frame
• Puts results in 2 buffers, which is total overkill for most cases
• Requires confirmation to exit

2. Diffs only the last value in a multi-=:

Try w/:

(deftest diff-test
  (is (= {:a 1 :b 2}
         {:a 2 :b 3}
         {:b 4 :c 5})))

3. Compares results textually, which could be screwed up by indentation, map key order, etc.

[bbatsov]

@xiongtx I'm sold. :-)

[bbatsov]

This should be under "New Features". :-)

[xiongtx]

✅

[bbatsov]

I think you meant to remove this - now we have two "New features" sections.

[xiongtx]

🤦‍♂️ ✅