handle PEP 639 License-Expression in test metadata (#46)

Author: nolith

tests/test_metadata.py

@@ -9,4 +9,6 @@ def test_resolve_distribution_information():
     fake_plugin_spec = PluginSpec("foo", "bar", pytest.fixture)
     dist = resolve_distribution_information(fake_plugin_spec)
     assert dist.metadata["Name"] == "pytest"
-    assert dist.metadata["License"] == "MIT"
+    # Support both legacy License field and PEP 639 License-Expression
+    license_value = dist.metadata.get("License-Expression") or dist.metadata.get("License")
+    assert license_value == "MIT"