Test resilience to missing wasm Updates.xml files

Makes sure that MetadataFactory can still produce a list of
architectures when the standard Updates.xml file is present, but the
expected wasm Updates.xml file is not. This should prevent failures
in the future if the Qt devs decide to change the way WASM works, as
they did with Qt 6.5.0.

tests/test_list.py

@@ -491,6 +491,29 @@ def test_list_qt_cli(
     assert output_set == expect_set
 
 
+def test_list_missing_wasm_updates(monkeypatch, capsys):
+    """Require that MetadataFactory is resilient to missing wasm updates.xml files"""
+    data_dir = Path(__file__).parent / "data"
+    expect = set(json.loads((data_dir / "windows-620-expect.json").read_text("utf-8"))["architectures"])
+
+    def _mock_fetch_http(_, rest_of_url, *args, **kwargs: str) -> str:
+        htmltext = (Path(__file__).parent / "data" / "windows-desktop.html").read_text("utf-8")
+        if rest_of_url.endswith("windows_x86/desktop/"):
+            return htmltext
+        elif rest_of_url.endswith("windows_x86/desktop/qt6_620/Updates.xml"):
+            return (data_dir / "windows-620-update.xml").read_text("utf-8")
+        else:
+            raise ArchiveDownloadError(f"No such file at {rest_of_url}")
+
+    monkeypatch.setattr(MetadataFactory, "fetch_http", _mock_fetch_http)
+
+    cli = Cli()
+    rv = cli.run("list-qt windows desktop --arch 6.2.0".split())
+    assert rv == 0
+    out, err = capsys.readouterr()
+    assert set(out.strip().split()) == expect
+
+
 @pytest.mark.parametrize(
     "qt_ver_str, expect_set", (("6.2.0", {"android_x86", "android_x86_64", "android_armv7", "android_arm64_v8a"}),)
 )