insert subscription, db test isolation

src/main.rs

@@ -6,10 +6,10 @@ use zero2prod::startup::run;
 #[tokio::main]
 async fn main() -> std::io::Result<()> {
     let config = get_configuration().expect("Failed to read configuration");
-	let connection = PgPoolOptions::new()
+	let connection_pool = PgPoolOptions::new()
     .max_connections(10).connect(&config.database.connection_string()).await.expect("Failed to connect to Postgres.");
 
     let address = format!("127.0.0.1:{}", config.application_port);
     let listener = TcpListener::bind(address).expect("Failed to bind random port");
-    run(listener, connection)?.await
+    run(listener, connection_pool)?.await
 }