Introduce jest snapshot testing utils (fixes #135)

[dogoku]

The main benefit of this PR is actually the applyTransform function, since it can be used for a lot of things.

• Refactored runInlineTest and extracted applyTransform function
• Introduced runSnapshotTest, same as runInlineTest but takes no expectedOutput
• Introduced defineSnapshotTest, same as defineInlineTest but takes no expectedOutput
• runInlineTest and runSnapshopTest now both also return the result applyTransform
  • This can be used to take the result of one run and use it for another test (check for idempotent)

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[ericwooley]

Any chance for a bump on this. It's been hanging for quite a while, and would make life so much easier.

[Daniel15]

I can try to review this soon! In the meantime you might find the existing test utils useful.

[Hypnosphi]

I've published this fork as a temporary scoped package: https://www.npmjs.com/package/@hypnosphi/jscodeshift

[Daniel15]

Seems reasonable to me.

[Hypnosphi]

@jbrown215 does 0.7.0 include this? If so, can you please mention it in the changelog?

[Daniel15]

Looks like it's included: v0.6.4...v0.7.0

[jbrown215]

@Hypnosphi: Yes and yes

[Daniel15]

For what it's worth, I was just writing a transform today and really like that you separated out applyTransform method, because it means I can use it for inline snapshots (which I prefer over 'regular' snapshots). Thanks! :D

const {applyTransform} = require('jscodeshift/dist/testUtils');
const fooToBar = require('../fooToBar');

function transform(input, options = null) {
  return applyTransform(fooToBar, options, {source: input});
}

test('first', () => {
  expect(
    transform(`foo()`),
  ).toMatchInlineSnapshot(`"bar();"`);
});