Add a note about testing jar

docs/testing.md

@@ -0,0 +1,14 @@
+# Unit testing with Hollow objects
+
+Hollow provides a `hollow-test` jar that contains some testing utilities to facilitate unit testing with Hollow objects.
+
+### HollowReadStateEngineBuilder
+
+This class allows easy creation of `HollowReadStateEngine` objects for use in unit tests.
+
+```java
+HollowReadStateEngine engine = new HollowReadStateEngineBuilder()
+    .add(new Movie("foo"))
+    .add(new Actor("bar"))
+    .build()
+```

mkdocs.yml

@@ -15,6 +15,7 @@ pages:
   - Interacting with a Hollow Dataset: 'interacting-with-a-dataset.md'
   - Data Ingestion: 'data-ingestion.md'
   - Advanced Topics: 'advanced-topics.md'
+  - Testing: 'testing.md'
   - Glossary: 'glossary.md'
   - Community: 'community.md'
   - Acknowledgements: 'acknowledgements.md'