Add docs for new snowplow matcher

doc/development/testing_guide/best_practices.md

@@ -895,6 +895,21 @@ When you want to ensure that no event got called, you can use `expect_no_snowplo
   end
 ```
 
+#### Test Snowplow context with the schema
+
+We added a [snowplow schema matcher](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60480)
+which accepts `schema path` and the `context`.
+
+We performed following steps to add a schema matcher spec:
+
+1. After adding a new schema in [Iglu repository](https://gitlab.com/gitlab-org/iglu),
+copy the same schema to `spec/fixtures/product_intelligence/` directory.
+1. From the schema, remove `"$schema"` key and value. We do not need it for specs
+and spec fails if we keep the key as it tries to look for the schema in the URL.
+1. Use the following snippet to call the matcher:
+```rb
+match_snowplow_context_schema(schema_path: '<filename from step 1>', context: <Context Hash> )
+```
 ### Table-based / Parameterized tests
 
 This style of testing is used to exercise one piece of code with a comprehensive