Validate Requires-Python metadata against the "mindeps" build in CI config

.github/workflows/build.yaml

@@ -85,3 +85,5 @@ jobs:
         run: python -m pip install -U tox
       - name: check package metadata
         run: python -m tox -e twine-check,poetry-check
+      - name: check min version is tested in CI
+        run: python -m tox r -e check-min-python-is-tested

scripts/ensure_min_python_is_tested.py

@@ -0,0 +1,63 @@
+# this script should only be called via
+#    tox run -e check-min-python-is-tested
+#
+# no other usages are supported
+import pathlib
+import subprocess
+import sys
+
+import ruamel.yaml
+
+YAML = ruamel.yaml.YAML(typ="safe")
+REPO_ROOT = pathlib.Path(__file__).parent.parent
+
+proc = subprocess.run(
+    ["python", "-m", "mddj", "read", "requires-python", "--lower-bound"],
+    check=True,
+    capture_output=True,
+    cwd=REPO_ROOT,
+)
+requires_python_version = proc.stdout.decode().strip()
+
+with open(REPO_ROOT / ".github" / "workflows" / "build.yaml") as f:
+    workflow = YAML.load(f)
+    try:
+        test_mindeps_job = workflow["jobs"]["test-mindeps"]
+    except KeyError:
+        raise ValueError("Could not find the test-mindeps job. Perhaps it has moved?")
+
+    job_steps = test_mindeps_job["steps"]
+    for step in job_steps:
+        if "uses" in step and "actions/setup-python" in step["uses"]:
+            setup_python_step = step
+            break
+    else:
+        raise ValueError("Could not find the setup-python step.")
+
+    python_version = setup_python_step["with"]["python-version"]
+    if python_version != requires_python_version:
+        print("ERROR: ensure_min_python_is_tested.py failed!")
+        print(
+            f"\nPackage data sets 'Requires-Python: >={requires_python_version}', "
+            f"but the test-mindeps job is configured to test '{python_version}'.\n",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+
+
+proc = subprocess.run(
+    ["python", "-m", "mddj", "read", "tox", "min-version"],
+    check=True,
+    capture_output=True,
+    cwd=REPO_ROOT,
+)
+tox_min_python_version = proc.stdout.decode().strip()
+if tox_min_python_version != requires_python_version:
+    print("ERROR: ensure_min_python_is_tested.py failed!")
+    print(
+        f"\nPackage data sets 'Requires-Python: >={requires_python_version}', "
+        "but tox is configured to test with a minimum of "
+        f"'{tox_min_python_version}'.\n",
+        file=sys.stderr,
+    )
+    sys.exit(1)

tox.ini

@@ -121,6 +121,14 @@ commands =
     py311: pip-compile --strip-extras -q -U --resolver=backtracking docs.in -o py{py_dot_ver}/docs.txt
     py311: pip-compile --strip-extras -q -U --resolver=backtracking typing.in -o py{py_dot_ver}/typing.txt
 
+[testenv:check-min-python-is-tested]
+description = Check the Requires-Python metadata against CI config
+skip_install = true
+deps =
+    ruamel.yaml<0.18
+    mddj==0.0.6
+commands = python scripts/ensure_min_python_is_tested.py
+
 [testenv:prepare-release]
 skip_install = true
 deps = scriv