[WIP] Initial support for passing back fixits with --json

[orta]

Summary

I'd like the Jest runner to provide enough information so that jest-editor-support or a watcher plugin could provide an implementation of a fixit. Re: #4442

So for this test:

it('!!!!!!!!!', () => {
  expect(1).toEqual(2);
});

It would result in this JSON:

{
  ...
  "testResults": [
    {
      "assertionResults": [
        {
          "ancestorTitles": [],
          "failureMessages": [
            "Error: ..."
          ],
          "fixits": [
            {
              "expected": {"value": 1},
              "message": "Update value from ${received} to ${expected}",
              "received": {"value": 2},
              "type": "number"
            }
          ],
          "fullName": "!!!!!!!!!",
          "location": null,
          "status": "failed",
          "title": "!!!!!!!!!"
        }
      ],
      "endTime": 1520173114536,
      "message":"...",
      "name":
        "/Users/orta/dev/projects/jest/jest2/packages/expect/src/fixits/__tests__/to_equal.test.js",
      "startTime": 1520173114238,
      "status": "failed",
      "summary": ""
    }
  ],
  "wasInterrupted": false
}

Things that are still a bit ambiguous

The data here is going to need to be enough to have an AST runner dig through the tree to find the right expect and subsequent assertion.

So in this case:

• Look for the test/it with the same name
• Loop through all the matchers in that test for the one with the same name
• Look at the matcher's parameters to see if there's a number primitive e.g. 1 not a variable
• Use that to offer a way to edit the source code

I feel like the fixit should probably include the matcher name, and maybe I could even include the first line of the error'd stack trace in there to provide a way to verify that the change is on the right one

{
  "expected": {"value": 1},
  "message": "Update value from ${received} to ${expected}",
  "received": {"value": 2},
  "type": "number",

  "matcher": "toEqual"
  "line": 231
}

Test plan

Would like to add an integration test to verify the whole system

[SimenB]

We have the stack of all expects seeing as they work by throwing. Only issue with that is potentially sourcemaps.
I'm quite excited by the possibilities here :)

[SimenB]

@orta can we close this seeing as inline snapshots are merged? Or do you still want this?

[SimenB]

Inline snapshots are good for this. We can revisit later if we want to extend the functionality for toBe, toEqual etc

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