DocumentImporter exposed a package-private openFileStream(File) so a
Mockito spy could force the IO-error branch of isPdfMagicBytes. The
test-only seam leaked into production: the method existed for testing,
not for any production extensibility.
Replace with a constructor-injected FileStreamOpener interface (single
abstract method, @FunctionalInterface) and a one-line
@Component DefaultFileStreamOpener delegate. Tests now inject a mock
opener instead of spying on the importer itself, which is also a more
idiomatic Mockito usage.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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