tests: fully type the test suite (#2794)

* tests: fully type the test suite

* chore: require more typing

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

test/test_environment.py

@@ -2,6 +2,7 @@ import os
 import subprocess
 import sys
 import textwrap
+from pathlib import Path
 
 import pytest
 
@@ -33,7 +34,7 @@ project_with_environment_asserts = test_projects.new_c_project(
 )
 
 
-def test(tmp_path):
+def test(tmp_path: Path) -> None:
     python_echo = f"'{sys.executable}' -c \"import sys; print(*sys.argv[1:])\""
     project_dir = tmp_path / "project"
     project_with_environment_asserts.generate(project_dir)
@@ -55,7 +56,7 @@ def test(tmp_path):
     assert set(actual_wheels) == set(expected_wheels)
 
 
-def test_overridden_path(tmp_path, capfd):
+def test_overridden_path(tmp_path: Path, capfd: pytest.CaptureFixture[str]) -> None:
     project_dir = tmp_path / "project"
     output_dir = tmp_path / "output"
 
@@ -108,7 +109,7 @@ def test_overridden_path(tmp_path, capfd):
         ),
     ],
 )
-def test_overridden_pip_constraint(tmp_path, build_frontend):
+def test_overridden_pip_constraint(tmp_path: Path, build_frontend: str) -> None:
     """
     Verify that users can use PIP_CONSTRAINT to specify a specific version of
     a build-system.requires dependency, by asserting the version of pytz in the