test: enable mypy typing checks for test/components/extractors/

[abhati27]

Related Issues

• part of Run typing checks on our test files #10396

(Deliberately not a closing keyword — #10396 tracks ~19 directories and only this one is covered here. It got auto-closed by #12272 and had to be reopened, so flagging it.)

Proposed Changes:

Adds test/components/extractors/ to the types target in pyproject.toml and fixes the six type errors it surfaced. No changes to haystack source — test typing fixes plus the allowlist entry only.

• test_regex_text_extractor.py — annotate the empty message list as list[ChatMessage], and ignore the arg-type on the call that deliberately passes a list[str] to assert the TypeError.
• test_llm_metadata_extractor.py — ignore the call-arg on the constructor call that deliberately omits chat_generator to assert the TypeError, and narrow _chat_generator with isinstance before calling to_dict(), since the ChatGenerator protocol does not declare it.
• image/test_llm_document_content_extractor.py — the same call-arg ignore for the missing-chat_generator case, and bind Document.content to a local before len() so the str | None is narrowed.

How did you test it?

$ hatch run test:types
Success: no issues found in 432 source files

$ hatch run test:unit test/components/extractors/
85 passed, 5 deselected in 5.39s

$ hatch run fmt
All checks passed!
6321 files left unchanged

hatch run test:types is the full CI target, not just the new directory.

Notes for the reviewer

One non-mechanical change worth a look: in test_from_dict_openai, the assertion is on extractor._chat_generator.to_dict(), but the attribute is typed as the ChatGenerator protocol, which doesn't declare to_dict. Rather than silence it, I narrowed with assert isinstance(extractor._chat_generator, OpenAIChatGenerator). That satisfies mypy and also pins that from_dict rebuilt an OpenAIChatGenerator, which is what the test is named for — the protocol-vs-implementation gap this issue was opened to surface.

The three type: ignores are all deliberate negative tests, and each sits directly under the pytest.raises(TypeError) that explains it — consistent with how #12318 (joiners) and #11859 (embedders) handled the same situation.

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings. — n/a, test-only typing change with no behavior or public API change
• I've used one of the conventional commit types for my PR title.
• I have documented my code.
• I have added a release note file. — n/a, tests/CI only and not user-facing; the previous increments (test: enable mypy typing checks for test/components/writers/ #12272, test: enable mypy typing checks for test/components/joiners/ #12318, test: enable mypy typing checks for four already-clean test directories #12333) didn't include one either
• I have run pre-commit hooks and fixed any issue.

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[Copilot]

Pull request overview

• Extends the test:types mypy target to include test/components/extractors/ and applies small typing-only adjustments in extractor tests so mypy passes without touching haystack runtime code.

Changes:

• Add test/components/extractors/ to the types script target list in pyproject.toml.
• Fix mypy errors in extractor tests via explicit annotations, narrowing, and scoped # type: ignore[...] for deliberate negative tests.
• Strengthen one test assertion by pinning from_dict() to rebuild an OpenAIChatGenerator instance.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
pyproject.toml	Adds test/components/extractors/ to the types (mypy) target paths.
test/components/extractors/test_regex_text_extractor.py	Annotates an empty messages list as list[ChatMessage] and scopes an ignore for an intentional type error test.
test/components/extractors/test_llm_metadata_extractor.py	Adds a scoped ignore for an intentional constructor misuse and narrows _chat_generator before calling implementation-specific APIs.
test/components/extractors/image/test_llm_document_content_extractor.py	Adds a scoped ignore for an intentional constructor misuse and narrows Document.content before len().

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