Fix psycopg2 instrument issue

instrumentation/opentelemetry-instrumentation-psycopg2/tests/test_psycopg2_integration.py

@@ -54,6 +54,7 @@ class MockConnection:
 
     def __init__(self, *args, **kwargs):
         self.cursor_factory = kwargs.pop("cursor_factory", None)
+        self._initialized = True
 
     def cursor(self):
         if self.cursor_factory:
@@ -63,6 +64,17 @@ def cursor(self):
     def get_dsn_parameters(self):  # pylint: disable=no-self-use
         return {"dbname": "test"}
 
+    def __setattr__(self, name, value):
+        """
+        This method is overridden to prevent adding new attributes to the MockConnection object.
+        At runtime, the psycopg2 connection object does not have attribute
+        _is_instrumented_by_opentelemetry, it will throw AttributeError when setting this
+        attribute.
+        """
+        if hasattr(self, '_initialized') and not hasattr(self, name):
+            raise AttributeError(f"Cannot add new attribute '{name}' to MockConnection")
+        super().__setattr__(name, value)
+
 
 class TestPostgresqlIntegration(TestBase):
     def setUp(self):