docs: Improve test command instructions in CLAUDE.md

Simplify test commands by exporting database URL at session start
instead of using inline environment variables. This avoids permission
prompts and makes commands cleaner.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: fubhy

CLAUDE.md

@@ -19,14 +19,19 @@ Graph Node is a Rust-based decentralized blockchain indexing protocol that enabl
 
 ### Testing
 
+⚠️ **IMPORTANT**: Always export the database URL at the start of each session:
 ```bash
-# Run unit tests (integration tests are excluded due to missing environment dependencies)
-# Claude should set the database URL before running tests:
 export THEGRAPH_STORE_POSTGRES_DIESEL_URL="postgresql://graph:graph@127.0.0.1:5432/graph-test"
+```
+
+Then run tests normally:
+```bash
+# Run unit tests (integration tests are excluded due to missing environment dependencies)
 cargo test --workspace --exclude graph-tests
 
-# Or run inline:
-THEGRAPH_STORE_POSTGRES_DIESEL_URL="postgresql://graph:graph@127.0.0.1:5432/graph-test" cargo test <test_name>
+# Run specific tests
+cargo test --package graph data_source::common::tests
+cargo test <specific_test_name>
 ```
 
 ### Code Quality