Summary

Add return type annotations and full type hints to all test files, then remove the disallow_untyped_defs = false mypy override for tests.* so strict typing is enforced going forward.

Motivation

The pyproject.toml currently relaxes mypy for tests:

[[tool.mypy.overrides]]
module = "tests.*"
disallow_untyped_defs = false

This lets untyped test functions accumulate silently. As of now there are 219 mypy errors across 24 test files — a manageable amount. If we wait, this number will grow with every new test file, making the eventual cleanup much more painful.

Scope

• Add -> None return annotations to all test functions and fixtures
• Add parameter type annotations where missing (fixture args, parametrize helpers, etc.)
• Fix any type-arg, arg-type, attr-defined, no-untyped-call errors that surface
• Remove the disallow_untyped_defs = false override from pyproject.toml
• Verify uv run mypy src/ tests/ passes with zero errors

Current error breakdown

Found 219 errors in 24 files (checked 67 source files)

Common error categories:

• no-untyped-def: missing -> None on test functions
• type-arg: missing generic type parameters (list → list[Any])
• attr-defined: accessing attributes on BaseException instead of typed error classes
• arg-type: dict invariance issues (dict[str, SubClass] vs dict[str, BaseClass])

Acceptance criteria

• uv run mypy src/ tests/ passes with zero errors
• disallow_untyped_defs = false override removed from pyproject.toml
• All existing tests still pass
• CI enforces typed tests going forward