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

[atikulmunna]

Related Issues

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

Proposed Changes:

Adds test/components/routers/ to the mypy target and fixes the 63 errors it surfaced.

Most of them came from route lists being inferred as list[dict[str, object]] where list[Route] is expected. Annotating those literals clears 26 errors by itself, and because Route is a TypedDict it also means mypy now checks each route against the real schema (condition, output, output_name, output_type) rather than accepting any dict.

The routes that are deliberately malformed keep a narrow type: ignore naming the specific violation, for example typeddict-item for a missing key and typeddict-unknown-key for an extra one. Being wrong is what those tests assert, and the error code documents which kind of wrong.

Three other things:

• test_metadata_router now asserts the concrete type of routed items before reading .data or .content. That narrows the Document | ByteStream union and also covers something the tests did not previously check.
• test_file_router called output.get(key) and then len() on the result. Those assertions require the key to be present, so they now index directly. It types cleanly and fails more clearly when a key is missing.
• __haystack_input__ / __haystack_output__ keep type: ignore[attr-defined], matching how test/core/component/test_component.py and test/components/generators/chat/test_llm.py already handle the attributes the @component decorator adds at runtime.

How did you test it?

All through hatch, on Python 3.10:

• hatch run test:types gives Success: no issues found in 434 source files
• hatch run fmt-check gives All checks passed!
• hatch run test:unit test/components/routers gives 104 passed, 30 skipped
• pre-commit run over the changed files: all applicable hooks pass

Notes for the reviewer

Annotating the routes surfaced two signatures that look narrower than the code they describe. I have not touched either, since both are public and this is a test-only change, but they may be worth a follow-up:

1. Route.output_type is type | list[type], which does not cover everything ConditionalRouter accepts. conditional_router.py has an explicit branch for "Union types (including Optional and X | Y syntax)", and there are passing tests using Callable[[int, str], bool] and list[str] | dict[str, int] | None as an output_type. Neither is a type, so both need an ignore today.

2. MetadataRouter.run takes list[Document] | list[ByteStream], which excludes a mixed list. test_run_with_mixed_documents_and_byte_streams passes exactly that and it works at runtime, so that call needs an ignore too.

Happy to open a PR for either if you think the annotations should be widened.

Checklist

• I have read the contributors guidelines and the code of conduct.
• I've used one of the conventional commit types for my PR title: test:.
• I have run pre-commit hooks and fixed any issue.
• n/a Unit tests and docstrings: this adds type annotations and a few assertions to existing tests, there is no new behavior to cover.
• n/a Release note: test-only change, not user-facing.

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[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/core/pipeline
pipeline.py
Project Total

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