Prefer license expression

Author: PalmtopTiger

src/pipdeptree/_models/package.py

@@ -39,10 +39,10 @@ def licenses(self) -> str:
         except PackageNotFoundError:
             return self.UNKNOWN_LICENSE_STR
 
-        license_strs: list[str] = []
         if license_str := dist_metadata.get("License-Expression"):
-            license_strs.append(license_str)
+            return f"({license_str})"
 
+        license_strs: list[str] = []
         classifiers = dist_metadata.get_all("Classifier", [])
         for classifier in classifiers:
             line = str(classifier)

tests/_models/test_package.py

@@ -148,10 +148,10 @@ def test_dist_package_as_dict() -> None:
             Mock(
                 get=lambda *args, **kwargs: "MIT",  # noqa: ARG005
                 get_all=lambda *args, **kwargs: [  # noqa: ARG005
-                    "License :: OSI Approved :: GNU General Public License v2 (GPLv2)",
+                    "License :: OSI Approved :: MIT License",
                 ],
             ),
-            "(MIT, GNU General Public License v2 (GPLv2))",
+            "(MIT)",
             id="license-expression-with-license-classifier",
         ),
     ],