Doc: add README for test (#12728)

### What problem does this PR solve?

We added instructions on how to test RAGFlow in test/README.md.

### Type of change

- [x] Documentation Update

test/README.md

@@ -0,0 +1,98 @@
+
+---
+
+### (1). Deploy RAGFlow services and images
+
+[https://ragflow.io/docs/build_docker_image](https://ragflow.io/docs/build_docker_image)
+
+### (2). Configure the required environment for testing
+
+**Install Python dependencies (including test dependencies):**
+
+```bash
+uv sync --python 3.12 --only-group test --no-default-groups --frozen
+
+```
+
+**Activate the environment:**
+
+```bash
+source .venv/bin/activate
+
+```
+
+**Install SDK:**
+
+```bash
+uv pip install sdk/python 
+
+```
+
+**Modify the `.env` file:** Add the following code:
+
+```env
+COMPOSE_PROFILES=${COMPOSE_PROFILES},tei-cpu
+TEI_MODEL=BAAI/bge-small-en-v1.5
+RAGFLOW_IMAGE=infiniflow/ragflow:v0.23.1 #Replace with the image you are using
+
+```
+
+**Start the container（wait two minutes）:**
+
+```bash
+docker compose -f docker/docker-compose.yml up -d
+
+```
+
+---
+
+### (3). Test Elasticsearch
+
+**a) Run sdk tests against Elasticsearch:**
+
+```bash
+export HTTP_API_TEST_LEVEL=p2
+export HOST_ADDRESS=http://127.0.0.1:9380  # Ensure that this port is the API port mapped to your localhost
+pytest -s --tb=short --level=${HTTP_API_TEST_LEVEL} test/testcases/test_sdk_api 
+
+```
+
+**b) Run http api tests against Elasticsearch:**
+
+```bash
+pytest -s --tb=short --level=${HTTP_API_TEST_LEVEL} test/testcases/test_http_api 
+
+```
+
+---
+
+### (4). Test Infinity
+
+**Modify the `.env` file:**
+
+```env
+DOC_ENGINE=${DOC_ENGINE:-infinity}
+
+```
+
+**Start the container:**
+
+```bash
+docker compose -f docker/docker-compose.yml down -v 
+docker compose -f docker/docker-compose.yml up -d
+
+```
+
+**a) Run sdk tests against Infinity:**
+
+```bash
+DOC_ENGINE=infinity pytest -s --tb=short --level=${HTTP_API_TEST_LEVEL} test/testcases/test_sdk_api 
+
+```
+
+**b) Run http api tests against Infinity:**
+
+```bash
+DOC_ENGINE=infinity pytest -s --tb=short --level=${HTTP_API_TEST_LEVEL} test/testcases/test_http_api 
+
+```