Support magic-assert with other assertion libraries

[novemberborn]

It'd be great if AVA could recognize assertion errors from other libraries and show similar output as it does for AVA's own assertions. See #1256 (comment).

[danny-andrews]

I second this. I'm using the fantastic expect library, and I get unhappy error messages like the following:

  /Users/danny/Projects/circleci-weigh-in/node_modules/expect/lib/assert.js:29

  Error thrown in test:

  Error {
    message: 'Expected { threshold: { targets: \'yoyo.js\', maxSize: 2, strategy: \'any\' }, offendingAssets: [ \'yoyo.js\' ] } to match { message: \'"yoyo.js" (35B) must be less than or equal to 2B!\', threshold: { targets: \'yoyo.js\', maxSize: 2, strategy: \'any\' }, offendingAssets: [ \'yoyo.js\' ] }',
  }

  assert (node_modules/expect/lib/assert.js:29:9)
  Expectation.toMatch (node_modules/expect/lib/Expectation.js:138:28)
  _ramda2.default.forEach (tests/bundle-size-utils.test.js:115:33)
  forEach (node_modules/ramda/src/forEach.js:43:5)
  Object.f2 [as forEach] (node_modules/ramda/src/internal/_curry2.js:25:16)
  Test.fn (tests/bundle-size-utils.test.js:113:9)

when using expect.toMatch

[tryzniak]

Are we still after this one? I'd like to tackle it, but need some hints :)
Edit:
I guess we just need to detect and format assertion errors here

ava/lib/test.js

Lines 364 to 370 in 49b202f

	if (!this.detectImproperThrows(result.error)) {
	this.saveFirstError(new assert.AssertionError({
	message: 'Error thrown in test',
	savedError: result.error instanceof Error && result.error,
	values: [formatErrorValue('Error thrown in test:', result.error)]
	}));
	}

[tryzniak]

Took a look at it and made some changes. What do you think about generation output as below? It for expect btw.
New version:

Old version:

[novemberborn]

I think you're on to something here @tryzniak. Would you mind opening a PR for this?

[tryzniak]

Sure! I'll do soon!