test(formatjs): Add regression test for issue #532 string concatenation in defaultMessage

[kdy1]

Fixes #532

Adds an explicit regression test reproducing the exact code from issue #532, verifying that string concatenation like 'Hello ' + 'world' in defaultMessage is properly evaluated rather than producing an empty array.

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[claude]

PR Review

This is a clean, focused regression test for issue #532. Here's my feedback:

What's good

• The test directly reproduces the exact code pattern from the issue (single-quoted strings, no description field)
• The comment linking to the issue (// Regression test for .../issues/532) is helpful for future reference
• The negative assertion expect(output).not.toMatch(/defaultMessage: \[\]/) clearly documents the specific failure mode (empty array instead of concatenated string)
• Follows the existing test file conventions

Observations

Distinction from existing test is intentional and important. There's already a similar test ("should handle string concatenation in defaultMessage") using double-quoted strings with a description field. The new test uses single-quoted strings without a description field — this appears to be the precise combination that triggered the bug. The distinction is valid.

Minor nit: The test name "should handle string concatenation in defaultMessage (issue #532)" is a bit redundant with the comment above it. Consider either dropping the (issue #532) suffix from the name (since the comment already links the issue) or dropping the comment. Not a blocker.

No changeset needed — test-only changes don't require version bumps, so the changeset-bot warning is expected and fine.

Summary

The regression test is correct, minimal, and appropriately targeted. No blocking issues.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Exercise AST mode in the regression test

I checked packages/formatjs/transform/src/lib.rs:893-905, and the defaultMessage: [] symptom only comes from the options.ast branch; with the default transformCode(input) call here, the plugin always prints a string literal instead. As written, this test can still pass while issue #532 remains broken for ast: true, so it doesn't actually cover the empty-array regression described in the comment/commit message.

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