jest-snapshot: Distinguish empty string from external snapshot not written

[pedrottimark]

Summary

When I tested the report for edge case that snapshot is empty string from custom serializer and received value is non-empty string, Jest confused it with new snapshot not written:

Fixed three places where the code distinguished snapshot from no snapshot:

• baseline: truthy versus falsey
• improved: string versus undefined (or nil, see Question) following example of code snippet:

    const hasSnapshot = isInline
      ? inlineSnapshot !== ''
      : this._snapshotData[key] !== undefined;

Question: What do you think about the conditional expression where undefined becomes null in the object that match returns? I am trying to keep the changes in complicated code to a minimum, but it fails the grep test to be able to find undefined :(

Residue:

• The test feedback above does not include the snapshot name
• Inline snapshots also have problems with empty string versus undefined

Test plan

The test does not save snapshots in CI mode by default still passes in e2e snapshot.test.ts

Also a local test of new snapshot with --ci option passed before and after

Here is the report when the local test fails for the correct reason:

I guess I had better get comfortable writing e2e tests for snapshots ;)

[codecov-io]

Codecov Report

Merging #8880 into master will increase coverage by 0.01%.
The diff coverage is 40%.

@@            Coverage Diff             @@
##           master    #8880      +/-   ##
==========================================
+ Coverage   64.11%   64.13%   +0.01%     
==========================================
  Files         275      275              
  Lines       11623    11623              
  Branches     2846     2844       -2     
==========================================
+ Hits         7452     7454       +2     
  Misses       3545     3545              
+ Partials      626      624       -2

Impacted Files	Coverage Δ
packages/jest-snapshot/src/State.ts	0% <0%> (ø)	⬆️
packages/jest-snapshot/src/index.ts	28.66% <66.66%> (+1.33%)	⬆️

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[SimenB]

A test would be nice 😀

[thymikee]

Small test maybe? :)

[pedrottimark]

Yes, after beating my head against the original e2e snapshot tests, I found the more recent tests, which I will adapt for this purpose tomorrow. It requires a new test because of custom serializer.

[pedrottimark]

Added e2e test to when expected external snapshot is empty string, then received value non-empty string causes ordinary test failure instead of bogus new snapshot not written

In the same file, I temporarily tested a future test (pardon pun) when expected internal snapshot is empty string, then received value non-empty string causes ordinary test failure instead of:

• overwriting snapshot without -u option
• new snapshot not written, if --ci option

Also added SnapshotReturnOptions type to verify that || '' was not needed

[github-actions]

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