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

[pedrottimark]

Summary

Breaking change: Add boolean isInline property to SnapshotMatchOptions so

• inlineSnapshot: undefined means internal snapshot not written instead of external snapshot
• inlineSnapshot: '' means empty string instead of internal snapshot not written

While trouble-shooting #8880 empty string in external snapshot, I found that internal snapshots had similar problem with different effect:

1. '--ci=false' when inline snapshot is empty string and received value is non-empty string, then instead of ordinary failure, test passes and replaces expected with received
2. '--ci=true' when inline snapshot was not written, test has ordinary failure with empty string as expected value

Edge case 1 requires custom serializer which writes empty string not enclosed in quote marks

Effect of change on dependent packages without TypeScript that do not upgrade a match call:

• external snapshot: no change, because absence of isInline means not inline
• internal snapshot: ignore inline snapshot, instead read and write as external snapshot

For what it’s worth, while reviewing GitHub repos for a subset of dependents on jest-snapshot I did found few calls to match method of SnapshotState and no calls to match inline snapshot

Test plan

Added 2 new e2e tests

Especially because of prettier update to inline snapshot tests, I changed the enclosing punctuation for literal strings from double quote to single quote

[codecov-io]

Codecov Report

Merging #8898 into master will increase coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #8898      +/-   ##
==========================================
+ Coverage   64.23%   64.24%   +0.01%     
==========================================
  Files         275      275              
  Lines       11658    11656       -2     
  Branches     2845     2844       -1     
==========================================
  Hits         7488     7488              
+ Misses       3546     3544       -2     
  Partials      624      624

Impacted Files	Coverage Δ
packages/jest-snapshot/src/State.ts	0% <0%> (ø)	⬆️
packages/jest-snapshot/src/index.ts	28.85% <0%> (+0.19%)	⬆️

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[SimenB]

I like it 🙂

[github-actions]

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