test: add getheader mock to account for fetch-content checking content-length

Author: jcristau

test/test_scripts_fetch_content.py

@@ -73,7 +73,13 @@ def mock_urlopen(req, timeout=None, *, cafile=None):
         # create a mock context manager
         cm = MagicMock()
         cm.getcode.return_value = 200
+
+        def getheader(field):
+            if field.lower() == "content-length":
+                return size
+
         # simulates chunking
+        cm.getheader = getheader
         cm.read.side_effect = [b"foo", b"bar", None]
         cm.__enter__.return_value = cm
         return cm