added description for macro __get_test_model_materialization

macros/artifacts/test/utilities/general/_general.yml

@@ -109,4 +109,8 @@ macros:
       But if there is a config.where presenting it will become the subquery:
       ```
       (select * from {database}.{schema}.{table} where {where}) as dbt_subquery
-      ```
+      ```
+  
+  - name: __get_test_model_materialization
+    description: |
+      Return the materialization type of the model being tested (eg: table, view, ephemeral etc).