Add a testcase for deterministic msgid order

tests/test_build_gettext.py

@@ -165,3 +165,18 @@ def test_gettext_template(app):
     result = (app.outdir / 'sphinx.pot').text(encoding='utf-8')
     assert "Welcome" in result
     assert "Sphinx %(version)s" in result
+
+
+@pytest.mark.sphinx('gettext', testroot='intl-template')
+def test_gettext_template_msgid_order_in_sphinxpot(app):
+    app.builder.build_all()
+    assert (app.outdir / 'sphinx.pot').isfile()
+
+    result = (app.outdir / 'sphinx.pot').text(encoding='utf-8')
+    assert re.search(
+        ('msgid "Template 1".*'
+         'msgid "This is Template 1\.".*'
+         'msgid "Template 2".*'
+         'msgid "This is Template 2\.".*'),
+        result,
+        flags=re.S)