Update README with test instructions and add unit tests

app/test_main.py

@@ -0,0 +1,24 @@
+from fastapi.testclient import TestClient
+from app.main import app
+import sys
+import os
+
+# Add the 'app' folder to the sys.path
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+
+from app.main import app  # Now this should work correctly
+
+client = TestClient(app)
+
+def test_home():
+    response = client.get("/")
+    assert response.status_code == 200
+    assert response.json() == {"message": "URL Shortener API"}
+
+def test_shorten_url():
+    response = client.post("/shorten", json={"url": "https://google.com"})
+    assert response.status_code == 200
+    data = response.json()
+    assert "short_url" in data
+    short_url = data["short_url"]
+    assert short_url.startswith("http://localhost:8000/")