chore: add test to confirm response-handles with multiple values for the same header name is supported

Author: Jake Champion

integration-tests/js-compute/fixtures/multiple-set-cookie/bin/index.js

@@ -45,7 +45,6 @@ routes.set('/', () => {
     h.append("Set-Cookie", "test9=9");
     h.append("Set-Cookie", "test10=10");
     h.append("Set-Cookie", "test11=11");
-    
     let r =  new Response("Hello", {
       headers: h
     });
@@ -67,4 +66,11 @@ routes.set('/', () => {
     r.headers.append("Set-Cookie", "test11=11");
     return r;
   });
+  routes.set("/multiple-set-cookie/downstream", async () => {
+    let response = await fetch('https://httpbin.org/cookies/set?1=1&2=2&3=3&4=4&5=5&6=6&7=7&8=8&9=9&10=10&11=11', {
+      backend: 'httpbin'
+    });
+
+    return new Response('', response);
+  });
 }

integration-tests/js-compute/fixtures/multiple-set-cookie/fastly.toml.in

@@ -10,3 +10,14 @@ service_id = ""
 
 [scripts]
   build = "node ../../../../js-compute-runtime-cli.js"
+
+[local_server]
+  [local_server.backends]
+    [local_server.backends.httpbin]
+      url = "https://httpbin.org/"
+
+[setup]
+  [setup.backends]
+    [setup.backends.httpbin]
+      address = "httpbin.org"
+      port = 443

integration-tests/js-compute/fixtures/multiple-set-cookie/tests.json

@@ -48,5 +48,30 @@
         ["Set-Cookie", "test11=11"]
       ]
     }
+  },
+  "GET /multiple-set-cookie/downstream": {
+    "environments": ["viceroy", "c@e"],
+    "downstream_request": {
+      "method": "GET",
+      "pathname": "/multiple-set-cookie/downstream"
+    },
+    "downstream_response": {
+      "status": 200,
+      "headers": [
+        ["Set-Cookie", "test=1; expires=Tue, 06-Dec-2022 12:34:56 GMT; Max-Age=60; Path=/; HttpOnly; Secure"],
+        ["Set-Cookie", "test_id=1; Max-Age=60; Path=/; expires=Tue, 06-Dec-2022 12:34:56 GMT"],
+        ["Set-Cookie", "test_id=1; Max-Age=60; Path=/; expires=Tue, 06-Dec-2022 12:34:56 GMT"],
+        ["Set-Cookie", "test2=2"],
+        ["Set-Cookie", "test3=3"],
+        ["Set-Cookie", "test4=4"],
+        ["Set-Cookie", "test5=5"],
+        ["Set-Cookie", "test6=6"],
+        ["Set-Cookie", "test7=7"],
+        ["Set-Cookie", "test8=8"],
+        ["Set-Cookie", "test9=9"],
+        ["Set-Cookie", "test10=10"],
+        ["Set-Cookie", "test11=11"]
+      ]
+    }
   }
 }