Jest Snapshot Version Header

[cpojer]

We discussed adding a header like:

// Jest Snapshot v1

and then validate Jest and throw if the snapshot version doesn't match, like:

Error: The snapshot file associated with this project is for version 1 but Jest 25 expects version 2.

[anilreddykatta]

@cpojer You mean everytime snapshot updates.increment new version?

[cpojer]

@anilreddykatta no, it's a version that we define in jest-snapshot, like:

const SNAPSHOT_VERSION = '1';

// later:
writeSnapshot() {
  const content = `// Jest Snapshot v${SNAPSHOT_VERSION}, <short url description>`
}

// readSnapshot
const content = readSnapshot();
if (snapshotVersionFromFirstLine < SNAPSHOT_VERSION) {
  throw new Error('update your snapshots!');
}

does that make sense?

[anilreddykatta]

@cpojer Yeah makes sense..so when we update snapshots next time..will the version number change?

[thymikee]

Yes. This is just to let you know, that there's a change in snapshot formatting, which you should just update, because it breaks your tests

[anilreddykatta]

@thymikee Thanks 👍

[kentaromiura]

can we add something like

exports['Schema Version'] = 1;

Instead of a comment? (as it's easier to get it for checks later)

[thymikee]

What about naming collision, when someone names the snapshot the same way?

[cpojer]

I think a comment is way more correct for this use case.

…

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[thymikee]

Maybe for first version we should not throw an error? We could just save the information about the version 1 in Jest 19 and error on future changes, what do you think?

[cpojer]

It should definitely throw an error in the first version. If Jest doesn't detect this header, throw -> it means you are pre Jest 19 and the snapshot must be updated.

[thymikee]

BTW, I'll be working on this tomorrow, but if anyone has time to deal with it today, don't hesitate!

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