Print output when snapshots are updated

[jednano]

Description

Notify when a snapshot update is available to match Jest snapshot behavior.

New snapshot summary (bold in green 📗)

• 1 snapshot written in 1 test suite.

Obsolete/failed snapshot summary (bold in red 📙)

• 1 obsolete snapshot found, press u to remove them.
• 1 obsolete snapshot file removed.
• 1 snapshot test failed in 1 test suite. Inspect your code changes or press u to update them.

[novemberborn]

Besides familiarity with Jest, could you elaborate on why you'd find this information useful?

• New snapshot files would be apparent in source control
• We report snapshot failures already, and we're working on printing the available commands in watch mode (Print watch mode shortcut commands #1525)
• We have an open issue for removing obsolete snapshot files (Remove snapshot files when a test file stops using snapshots #1424) but again I think source control is sufficient here

[jednano]

Sometimes I add or change a test and it gets appended to the end of the snapshot Markdown file. If I hit u then it refreshes the whole Markdown file and the snapshot that was previously at the end of the file is now somewhere in the middle. This isn't obvious, because there's no messaging that tells me my snapshots need to be updated. Technically, the snapshot itself perhaps doesn't need to be updated, but the Markdown file does (at least). I need some kind of indicator to tell me it's time to hit u so I can ensure my Markdown file won't change with a subsequent test run. In other words, the watch command shouldn't be yielding a different Markdown file than if I were to hit u or do a normal, non-watch test run. Does that make sense?

[novemberborn]

Ah. The Markdown file is appended to, rather than rewritten, for performance reasons. It's not used by AVA though. I don't know how big of a problem this is, but then to be honest I tend to explicitly update snapshots before committing them.

This isn't obvious, because there's no messaging that tells me my snapshots need to be updated. Technically, the snapshot itself perhaps doesn't need to be updated, but the Markdown file does (at least).

They don't need to be updated manually, though I appreciate you're trying to avoid extraneous changes in the future when you're explicitly updating snapshots for unrelated reasons.

[jednano]

Yeah I realize the Markdown files are not used by AVA, but AVA does produce two different results for the Markdown file, depending on watch vs. normal run, as you mentioned, for performance reasons. That's fine. I just wish there were some notification that it needs a hard re-write (an update) in the watch scenario. You explicitly update snapshots before committing and so do I for this very reason, but if it were more clear, we wouldn't have to be so trigger happy w/ the updates.

[novemberborn]

Right so you're saying you'd like a reminder from AVA that snapshots were modified, so you can immediately rebuild them. That makes sense I think.

Note though that we shouldn't communicate "and now update your snapshots", since everything is working fine. This is for those of us who can't abide the thought of future churn in the Markdown files 😉

[jednano]

Agreed. That would be misleading. Perhaps a message like:

Appended 2 snapshots to Markdown files. Press u to update.

I'm not sure how to be any more concise. The more verbose version would say "...to update/sync with snapshot order."

[novemberborn]

"Updated 2 snapshots" would be sufficient I think. Folks like us will catch on and know what to do, especially when we land #1525.