Add test for loading from wheel.

conftest.py

@@ -0,0 +1,14 @@
+import subprocess
+
+import pytest
+
+
+@pytest.fixture
+def static_wheel(tmp_path, monkeypatch):
+    subprocess.check_call(
+        ['pip', 'download', '--no-deps', '--dest', str(tmp_path), 'sampleproject'],
+        stderr=subprocess.DEVNULL,
+        stdout=subprocess.DEVNULL,
+    )
+    (wheel,) = tmp_path.iterdir()
+    monkeypatch.setenv('JARACO_PACKAGING_SPHINX_WHEEL', str(wheel))

jaraco/packaging/sphinx.py

@@ -36,6 +36,12 @@ def _load_metadata_from_wheel():
     If indicated by an environment variable, expect the metadat
     to be present in a wheel and load it from there, avoiding
     the build process. Ref jaraco/jaraco.packaging#7.
+
+    >>> _load_metadata_from_wheel()
+    >>> getfixture('static_wheel')
+    >>> meta = _load_metadata_from_wheel()
+    >>> meta['Name']
+    'sampleproject'
     """
     wheel = os.environ['JARACO_PACKAGING_SPHINX_WHEEL']
     (dist,) = metadata.distributions(path=[wheel])