Flash out API test suite

README.md

@@ -181,9 +181,32 @@ docker exec -it ppr_nextgen_db mysql -u ppr_user -p ppr_nextgen
 ```
 
 ### Testing
+The backend API tests use pytest, FastAPI's `TestClient`, and an isolated in-memory SQLite database with dependency overrides for database sessions and authenticated users.
+
+See [`backend/tests/README.md`](./backend/tests/README.md) for a module-by-module explanation of what the tests cover and why.
+
 ```bash
 cd backend
-pytest tests/
+pytest
+```
+
+Or, with the Docker development stack running:
+
+```bash
+docker compose exec api pytest
+```
+
+To inspect API test coverage:
+
+```bash
+cd backend
+pytest --cov=app --cov-report=term-missing
+```
+
+Or in Docker:
+
+```bash
+docker compose exec api pytest --cov=app --cov-report=term-missing
 ```
 
 ## Additional Features
@@ -293,4 +316,4 @@ docker-compose down
 To remove volumes (database data):
 ```bash
 docker-compose down -v
-```
+```