use squidclient for unit test

docker-compose.test.yml

@@ -1,11 +1,20 @@
 version: '2'
 services:
   proxy:
-    build: .
+    image: squidproxy
+    build:
+      context: .
+      dockerfile: Dockerfile
+    healthcheck:
+      test: ["CMD", "sh", "-exc", "squidclient -T 3 mgr:info 2> /dev/null | grep -qF '200 OK'"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+      start_period: 1s
   sut:
-    image: alpine:3.10.1
+    image: squidproxy
     links: 
       - proxy
     depends_on:
       - proxy
-    command: sh -exc "apk add --update curl && sleep 5 && exec curl --proxy http://proxy:3128 -I http://google.com/"
+    command: sh -exc "sleep 10 && squidclient -h proxy -T 3 'https://postman-echo.com/get?squidtest=ok' 2> /dev/null | grep -qF '200 OK'"