Only include xz --list --verbose output if the xz has no other differences.

diffoscope/comparators/xz.py

@@ -80,7 +80,7 @@ class XzFile(File):
         difference = super().compare(other, source)
 
         # Append xz --list *after* showing any container differences.
-        if isinstance(other, XzFile):
+        if difference and not difference.details and isinstance(other, XzFile):
             xz_list = Difference.from_operation(
                 XZList, self.path, other.path, source="xz --list"
             )

tests/comparators/test_xz.py

@@ -52,8 +52,6 @@ def differences(xz1, xz2):
 def test_content_source(differences):
     assert differences[0].source1 == "test1"
     assert differences[0].source2 == "test2"
-    assert differences[1].source1 == "xz --list"
-    assert differences[1].source2 == "xz --list"
 
 
 @skip_unless_tools_exist("xz")
@@ -67,14 +65,11 @@ def test_content_source_without_extension(tmpdir, xz1, xz2):
     difference = xz1.compare(xz2).details
     assert difference[0].source1 == "test1-content"
     assert difference[0].source2 == "test2-content"
-    assert difference[1].source1 == "xz --list"
-    assert difference[1].source2 == "xz --list"
 
 
 @skip_unless_tools_exist("xz")
 def test_content_diff(differences):
     assert_diff(differences[0], "text_ascii_expected_diff")
-    assert_diff(differences[1], "text_xz_list")
 
 
 @skip_unless_tools_exist("xz")