CCM-14205 - Added readme for performance tests

Author: rhyscoxnhs

tests/performance/README.md

@@ -0,0 +1,34 @@
+# performance
+
+Load tests for the client-callbacks service. These tests run against a real deployed AWS environment — they are not unit tests and cannot run locally without a live stack.
+
+## Prerequisites
+
+- AWS credentials configured for the target environment
+- The service deployed to the target environment
+
+## Environment Variables
+
+| Variable | Required | Default | Description |
+|---|---|---|---|
+| `ENVIRONMENT` | Yes | — | Target environment name (e.g. `dev`) |
+| `AWS_ACCOUNT_ID` | Yes | — | AWS account ID for the target environment |
+| `AWS_REGION` | No | `eu-west-2` | AWS region |
+| `PROJECT` | No | `nhs` | Project name prefix used in resource naming |
+| `COMPONENT` | No | `callbacks` | Component name used in resource naming |
+
+## Running
+
+From the repository root:
+
+```bash
+ENVIRONMENT=dev AWS_ACCOUNT_ID=123456789012 npm run test:performance --workspace tests/performance
+```
+
+## What the Tests Do
+
+The global setup creates a test client subscription config in the S3 subscription config bucket.
+
+The load test sends ~3,000 events/s to the SQS inbound queue for 30 seconds, then reads CloudWatch Logs to assert that the p95 Lambda processing time is below 500ms.
+
+The global teardown removes the test client subscription config from S3.