docs(tests): Add a bunch of documentation for our testing systems (#3139)

# What does this PR do?

Creates a structured testing documentation section with multiple detailed pages:

- Testing overview explaining the record-replay architecture
- Integration testing guide with practical usage examples
- Record-replay system technical documentation
- Guide for writing effective tests
- Troubleshooting guide for common testing issues

Hopefully this makes things a bit easier.

docs/source/contributing/index.md

@@ -4,11 +4,11 @@
 
 ## Adding a New Provider
 
-See the [Adding a New API Provider Page](new_api_provider.md) which describes how to add new API providers to the Stack.
+See:
+- [Adding a New API Provider Page](new_api_provider.md) which describes how to add new API providers to the Stack.
+- [Vector Database Page](new_vector_database.md) which describes how to add a new vector databases with Llama Stack.
+- [External Provider Page](../providers/external/index.md) which describes how to add external providers to the Stack.
 
-See the [Vector Database Page](new_vector_database.md) which describes how to add a new vector databases with Llama Stack.
-
-See the [External Provider Page](../providers/external/index.md) which describes how to add external providers to the Stack.
 ```{toctree}
 :maxdepth: 1
 :hidden:
@@ -19,11 +19,16 @@ new_vector_database
 
 ## Testing
 
-See the [Test Page](testing.md) which describes how to test your changes.
+
+```{include} ../../../tests/README.md
+```
+
+### Advanced Topics
+
+For developers who need deeper understanding of the testing system internals:
+
 ```{toctree}
 :maxdepth: 1
-:hidden:
-:caption: Testing
 
-testing
-```
+testing/record-replay
+```