Raise ValueError when cookie max-age is not an integer (#2001)

* Raise valueerror when cookie max-age is not an integer

tests/test_cookies.py

@@ -162,7 +162,7 @@ def test_cookie_set_same_key(app):
     assert response.cookies["test"] == "pass"
 
 
-@pytest.mark.parametrize("max_age", ["0", 30, 30.0, 30.1, "30", "test"])
+@pytest.mark.parametrize("max_age", ["0", 30, "30"])
 def test_cookie_max_age(app, max_age):
     cookies = {"test": "wait"}
 
@@ -204,6 +204,23 @@ def test_cookie_max_age(app, max_age):
         assert cookie is None
 
 
+@pytest.mark.parametrize("max_age", [30.0, 30.1, "test"])
+def test_cookie_bad_max_age(app, max_age):
+    cookies = {"test": "wait"}
+
+    @app.get("/")
+    def handler(request):
+        response = text("pass")
+        response.cookies["test"] = "pass"
+        response.cookies["test"]["max-age"] = max_age
+        return response
+
+    request, response = app.test_client.get(
+        "/", cookies=cookies, raw_cookies=True
+    )
+    assert response.status == 500
+
+
 @pytest.mark.parametrize(
     "expires", [datetime.utcnow() + timedelta(seconds=60)]
 )