Bug 1433390 - Use register_assert_rewrite to enable introspection in assertion helper. Pytest by default only loads test modules, and enables assert introspection for them. For any helper method which also uses asserts, only a plain assertion is printed. To enable introspection also for the assertion helper, the module has to be registered for assertion rewrite. MozReview-Commit-ID: 97JzuykXxWE

--- a/testing/web-platform/tests/webdriver/tests/__init__.py
+++ b/testing/web-platform/tests/webdriver/tests/__init__.py
@@ -0,0 +1,4 @@
+import pytest
+
+# Enable pytest assert introspection for assertion helper
+pytest.register_assert_rewrite('tests.support.asserts')