bpo-14465: Extend test to cover an argument error case.

scoder · scoder · commit 31d2ebba8747 · 2019-08-15T17:53:26.000+02:00
diff --git a/Lib/test/test_xml_etree.py b/Lib/test/test_xml_etree.py
@@ -875,6 +875,13 @@ def test_indent_space_caching(self):
 
     def test_indent_level(self):
         elem = ET.XML("<html><body><p>pre<br/>post</p><p>text</p></body></html>")
+        with self.assertRaises(ValueError):
+            ET.indent(elem, level=-1)
+        self.assertEqual(
+            ET.tostring(elem),
+            b"<html><body><p>pre<br />post</p><p>text</p></body></html>"
+        )
+
         ET.indent(elem, level=2)
         self.assertEqual(
             ET.tostring(elem),
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
@@ -1203,6 +1203,8 @@ def indent(tree, space="  ", level=0):
     """
     if isinstance(tree, ElementTree):
         tree = tree.getroot()
+    if level < 0:
+        raise ValueError(f"Initial indentation level must be >= 0, got {level}")
     if not len(tree):
         return
 
