diff --git a/testing/backend/unit/test_rate_limiter_check_scan_rate_limit.py b/testing/backend/unit/test_rate_limiter_check_scan_rate_limit.py
new file mode 100644
index 000000000..a119c52b9
--- /dev/null
+++ b/testing/backend/unit/test_rate_limiter_check_scan_rate_limit.py
@@ -0,0 +1,78 @@
+"""
+Unit tests for check_scan_rate_limit async dependency in rate_limiter.py.
+
+fastapi and redis.asyncio are available in the test environment, so the module
+can be imported and tested directly without sys.modules mocking.
+"""
+from unittest.mock import MagicMock, AsyncMock
+import pytest
+
+from backend.secuscan.rate_limiter import check_scan_rate_limit
+from fastapi import HTTPException
+
+
+class StubState:
+    """Minimal object that provides request.app.state.scan_rate_limiter."""
+    def __init__(self, limiter=None):
+        self.scan_rate_limiter = limiter
+
+
+class StubApp:
+    """Minimal object that provides request.app.state."""
+    def __init__(self, limiter=None):
+        self.state = StubState(limiter)
+
+
+class StubRequest:
+    """Minimal request object with headers and app.state."""
+    def __init__(self, headers=None, limiter=None):
+        self.headers = headers or {}
+        self.app = StubApp(limiter)
+
+
+class TestCheckScanRateLimit:
+    """Test the check_scan_rate_limit FastAPI dependency."""
+
+    @pytest.mark.asyncio
+    async def test_calls_limiter_check_when_limiter_is_set(self):
+        """When scan_rate_limiter is present in app.state, call limiter.check()."""
+        mock_limiter = AsyncMock()
+        mock_request = StubRequest(limiter=mock_limiter)
+
+        await check_scan_rate_limit(mock_request)
+
+        mock_limiter.check.assert_called_once_with(mock_request)
+
+    @pytest.mark.asyncio
+    async def test_raises_when_limiter_check_raises_httpexception(self):
+        """When limiter.check() raises HTTPException, it should propagate."""
+        mock_limiter = AsyncMock()
+        mock_limiter.check.side_effect = HTTPException(status_code=429, detail="rate limit")
+        mock_request = StubRequest(limiter=mock_limiter)
+
+        with pytest.raises(HTTPException) as exc_info:
+            await check_scan_rate_limit(mock_request)
+
+        assert exc_info.value.status_code == 429
+
+    @pytest.mark.asyncio
+    async def test_noop_when_limiter_is_none(self):
+        """When app.state.scan_rate_limiter is None, no-op without error."""
+        mock_request = StubRequest(limiter=None)
+
+        # Should not raise
+        await check_scan_rate_limit(mock_request)
+
+    @pytest.mark.asyncio
+    async def test_noop_when_state_is_absent(self):
+        """When request.app.state does not expose scan_rate_limiter, no-op."""
+        mock_request = MagicMock()
+        mock_request.app.configure_mock(state=MagicMock(spec=[]))
+        # Delete scan_rate_limiter so getattr falls back to None
+        del mock_request.app.state.scan_rate_limiter
+
+        limiter = getattr(mock_request.app.state, "scan_rate_limiter", None)
+        assert limiter is None
+
+        # Should not raise
+        await check_scan_rate_limit(mock_request)