re-use existing documentation

Author: szehon-ho

AGENTS.md

@@ -1,13 +1,14 @@
 # Apache Spark
 
-This file provides context and guidelines for AI agents working with the Apache Spark codebase.
+This file provides context and guidelines for AI coding assistants working with the Apache Spark codebase.
 
-## Build
+## Build and Test
 
-Prefer SBT via the wrapper script (not Maven):
-```bash
-./build/sbt compile
-./build/sbt "module/test"
-./build/sbt "module/testOnly *TestClassName"
-```
+Prefer building in sbt over maven:
 
+- **Building Spark**: [docs/building-spark.md](docs/building-spark.md)
+  - SBT build instructions: See the ["Building with SBT"](docs/building-spark.md#building-with-sbt) section
+  - SBT testing: See the ["Testing with SBT"](docs/building-spark.md#testing-with-sbt) section
+  - Running individual tests: See the ["Running Individual Tests"](docs/building-spark.md#running-individual-tests) section
+
+- **PySpark Testing**: [python/docs/source/development/testing.rst](python/docs/source/development/testing.rst)