Run tox tests in parallel

changes/1247.misc.rst

@@ -0,0 +1 @@
+Python tests are now run in parallel via ``tox``.

pyproject.toml

@@ -3,7 +3,9 @@ requires = ["setuptools>=60", "setuptools_scm[toml]>=7.0"]
 build-backend = "setuptools.build_meta"
 
 [tool.coverage.run]
+concurrency = ["multiprocessing", "thread"]
 parallel = true
+sigterm = true
 branch = true
 relative_files = true
 source_pkgs = ["briefcase"]

setup.cfg

@@ -91,8 +91,10 @@ install_requires =
 # ensure environment consistency.
 dev =
     coverage[toml] == 7.2.3
+    coverage-enable-subprocess == 1.0
     pre-commit == 3.2.2
     pytest == 7.3.1
+    pytest-xdist == 3.2.1
     setuptools_scm[toml] == 7.1.0
     tox == 4.4.12
 docs =

tests/conftest.py

@@ -55,7 +55,7 @@ def no_print(monkeypatch):
 
 @pytest.fixture
 def sleep_zero(monkeypatch):
-    """Replace all calls to ``time.sleep(x)`` with ``time.sleep(0)."""
+    """Replace all calls to ``time.sleep(x)`` with ``time.sleep(0)``."""
     monkeypatch.setattr(time, "sleep", lambda x: _sleep(0))
 
 

tox.ini

@@ -7,16 +7,19 @@ download = True
 # The leading comma generates the "py" environment.
 [testenv:py{,38,39,310,311,312}{,-coverage}]
 passenv =
-    # LOCALAPPDATA is needed to test data directory creation on Windows.
+    # Needed on Windows to test data directory creation
     LOCALAPPDATA
+setenv =
+    # Start Python such that coverage is possible in subprocesses
+    COVERAGE_PROCESS_START = {toxinidir}/pyproject.toml
 extras =
     dev
 # 2023-04-22 The virtualenv used by Tox has pip 23.1 pinned into it
 # This version has a bug on winstore installs of Python, so we
 # need to force pip to be updated.
 download = True
 commands =
-    python -m coverage run -m pytest -vv {posargs}
+    python -m coverage run -m pytest {posargs:-n auto -vv}
     coverage : python -m coverage combine
     coverage : python -m coverage report