feat(test): server setup and teardown for tests

- Application server will now be setup on EVERY test and closed after
that test

tests/health_check.rs

@@ -1,6 +1,10 @@
+// tokio spins up a new async runtime every time 
+// at the beginning of each test case and shutdown at
+// the end of each test case
+// the spawn_app() function therefore only survives as long as the runtime
 #[tokio::test]
 async fn health_check_works(){
-    spawn_app().await.expect("Failed to spawn our app.");
+    spawn_app();
 
     let client = reqwest::Client::new();
 
@@ -10,6 +14,11 @@ async fn health_check_works(){
     assert_eq!(Some(0), response.content_length());
 }
 
-async fn spawn_app() -> Result<(), std::io::Error> {
-    email_newsletter_api::run().await
+fn spawn_app() {
+    let server = email_newsletter_api::run().expect("Failed to bind address");
+    // run() returns an instance of HttpServer that will run forever.
+    // We don't want this behavior
+    // Therefore we want to spawn our server, run our test logic
+    // and then tear down the entire test suite
+    let _ = tokio::spawn(server);
 }