Refs #3331 -- integrated wycheproof ECDH tests (#4354)

* Refs #3331 -- integrated wycheproof ECDH tests

* flake8 + missing assert

* Handle this error case

* skip on unsupported

* shouldn't need to try here any more
diff --git a/tests/utils.py b/tests/utils.py
index ccc3b7c..b950f8b 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -906,6 +906,10 @@
     def acceptable(self):
         return self.testcase["result"] == "acceptable"
 
+    @property
+    def invalid(self):
+        return self.testcase["result"] == "invalid"
+
     def has_flag(self, flag):
         return flag in self.testcase["flags"]