diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_response_cache.py b/tests/test_response_cache.py
new file mode 100644
index 0000000..e28cdec
--- /dev/null
+++ b/tests/test_response_cache.py
@@ -0,0 +1,143 @@
+import unittest
+import time
+from src.proxy_server import ResponseCache
+
+
+class TestResponseCache(unittest.TestCase):
+    def setUp(self):
+        # Create a small cache for easier testing (1 MB max size)
+        self.cache = ResponseCache(max_mb=1)
+
+    def test_initial_state(self):
+        self.assertEqual(self.cache._size, 0)
+        self.assertEqual(self.cache.hits, 0)
+        self.assertEqual(self.cache.misses, 0)
+        self.assertEqual(self.cache._max, 1 * 1024 * 1024)
+
+    def test_cache_miss_and_hit(self):
+        url = "http://example.com/test.js"
+        response = b"console.log('test');"
+
+        # Initial miss
+        self.assertIsNone(self.cache.get(url))
+        self.assertEqual(self.cache.misses, 1)
+
+        # Put in cache
+        self.cache.put(url, response, ttl=60)
+        self.assertEqual(self.cache._size, len(response))
+
+        # Cache hit
+        cached_response = self.cache.get(url)
+        self.assertEqual(cached_response, response)
+        self.assertEqual(self.cache.hits, 1)
+
+    def test_expiration_eviction(self):
+        url = "http://example.com/expired.css"
+        response = b"body { background: red; }"
+
+        # Put with TTL of -1 (already expired)
+        self.cache.put(url, response, ttl=-1)
+        self.assertEqual(self.cache._size, len(response))
+
+        # Should be evicted during get
+        self.assertIsNone(self.cache.get(url))
+        self.assertEqual(self.cache.misses, 1)
+        self.assertEqual(self.cache._size, 0)
+        self.assertNotIn(url, self.cache._store)
+
+    def test_cache_eviction_when_full(self):
+        # max_size is 1MB = 1048576 bytes
+        # max // 4 is 262144 bytes
+        # Let's put 4 items of ~200KB each (under the 1/4 max limit individually)
+        chunk = b"A" * 200000
+
+        self.cache.put("url1", chunk, ttl=60)
+        self.cache.put("url2", chunk, ttl=60)
+        self.cache.put("url3", chunk, ttl=60)
+        self.cache.put("url4", chunk, ttl=60)
+
+        self.assertEqual(self.cache._size, 800000)
+        self.assertEqual(len(self.cache._store), 4)
+
+        # Put a 5th item to exceed 1MB total size
+        # 800000 + 250000 = 1050000 > 1048576 (1MB)
+        chunk5 = b"B" * 250000
+        self.cache.put("url5", chunk5, ttl=60)
+
+        # It should have evicted url1
+        self.assertNotIn("url1", self.cache._store)
+        self.assertIn("url2", self.cache._store)
+        self.assertIn("url3", self.cache._store)
+        self.assertIn("url4", self.cache._store)
+        self.assertIn("url5", self.cache._store)
+        self.assertEqual(self.cache._size, 850000)
+
+    def test_cache_replacement(self):
+        url = "http://example.com/replace.js"
+        response1 = b"12345"
+        response2 = b"123"
+
+        self.cache.put(url, response1, ttl=60)
+        self.assertEqual(self.cache._size, 5)
+
+        # Replace with smaller response
+        self.cache.put(url, response2, ttl=60)
+        self.assertEqual(self.cache._size, 3)
+        self.assertEqual(self.cache.get(url), response2)
+
+    def test_limits_rejection(self):
+        url = "http://example.com/reject.js"
+
+        # Test empty payload rejection
+        self.cache.put(url, b"", ttl=60)
+        self.assertEqual(self.cache._size, 0)
+        self.assertNotIn(url, self.cache._store)
+
+        # Test large payload rejection (> 25% of max)
+        # 1MB / 4 = 262144 bytes
+        large_response = b"C" * 262145
+        self.cache.put(url, large_response, ttl=60)
+        self.assertEqual(self.cache._size, 0)
+        self.assertNotIn(url, self.cache._store)
+
+    def test_parse_ttl(self):
+        # Test non-200 responses
+        non_200 = b"HTTP/1.1 404 Not Found\r\n\r\n"
+        self.assertEqual(ResponseCache.parse_ttl(non_200, "http://ex.com"), 0)
+
+        # Test no-store
+        no_store = b"HTTP/1.1 200 OK\r\nCache-Control: no-store\r\n\r\n"
+        self.assertEqual(ResponseCache.parse_ttl(no_store, "http://ex.com"), 0)
+
+        # Test explicit max-age
+        max_age = b"HTTP/1.1 200 OK\r\nCache-Control: max-age=120\r\n\r\n"
+        self.assertEqual(ResponseCache.parse_ttl(max_age, "http://ex.com"), 120)
+
+        # Test heuristic by extension (static asset)
+        ext = b"HTTP/1.1 200 OK\r\n\r\n"
+        self.assertEqual(ResponseCache.parse_ttl(ext, "http://ex.com/style.css"), 3600)
+        self.assertEqual(ResponseCache.parse_ttl(ext, "http://ex.com/img.png?v=1"), 3600)
+
+        # Test heuristic by Content-Type: image/font
+        ct_img = b"HTTP/1.1 200 OK\r\nContent-Type: image/jpeg\r\n\r\n"
+        self.assertEqual(ResponseCache.parse_ttl(ct_img, "http://ex.com/data"), 3600)
+
+        # Test heuristic by Content-Type: css/js
+        ct_css = b"HTTP/1.1 200 OK\r\nContent-Type: text/css; charset=utf-8\r\n\r\n"
+        self.assertEqual(ResponseCache.parse_ttl(ct_css, "http://ex.com/data"), 1800)
+
+        # Test dynamic content (html/json) default to 0
+        ct_html = b"HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n"
+        self.assertEqual(ResponseCache.parse_ttl(ct_html, "http://ex.com/data"), 0)
+
+        # Test unhandled content type
+        ct_other = b"HTTP/1.1 200 OK\r\nContent-Type: application/octet-stream\r\n\r\n"
+        self.assertEqual(ResponseCache.parse_ttl(ct_other, "http://ex.com/data"), 0)
+
+        # Test missing headers completely
+        missing_hdrs = b"HTTP/1.1 200 OK"
+        self.assertEqual(ResponseCache.parse_ttl(missing_hdrs, "http://ex.com"), 0)
+
+
+if __name__ == "__main__":
+    unittest.main()