Do not write snapshots by default on CI

[cpojer]

Summary

When running on a CI environment or with --ci, Jest will now refuse to write new snapshots. This is so that on CI, uncommitted snapshots will fail rather than pass by writing new files every time.

I introduced a --ci field and changed the updateSnapshot field into one of three states: none, all or new. None won't write any snapshot files, all will write all and clean snapshots up and new will only create new snapshots.

Test plan

• jest

[cpojer]

In the last commit, there are some unrelated changes because prettier was being funny. I think it's all fixed now and those are the properly printed values. Sorry for the churn there.

[kole]

Was this PR merged without any updates to the docs? I am getting the New snapshot was not written. The update flag must be explicitly passed to write a new snapshot. error in Travis and can't figure out how to get rid of it because there are no docs for how to correctly run snapshot tests in jest in a CI env.

P.S. I am adding the update flag... still getting this error.

[cpojer]

It seems like you aren't adding snapshots to your CI and therefore using snapshots wrongly. The documentation is on the website: http://facebook.github.io/jest/docs/en/snapshot-testing.html#snapshots-are-not-written-automatically-on-continuous-integration-systems-ci

[kole]

@cpojer I am still struggling here. It seems like the point of this change is to prevent snapshot checks from running in a CI environment, but I cannot figure out why that is a good idea. All my snapshots are committed in the repo. So a snapshot check should pass or fail just like it does in a local dev env, no?

I have also since removed the -u flag and that is where problems are happening. If I add the -u flag, tests pass fine, obviously. But I want the CI build to fail if the snapshot check fails.

Thanks in advance for your guidance.

[kole]

Never mind. I think I get it now. The point of the change is to not allow snapshots to be created in a CI env. To give snapshot changes a better chance to truly fail.

Sorry for the confusion.

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