docs: elaborate on test

Author: jsjoeio

test/unit/node/app.test.ts

@@ -75,7 +75,9 @@ describe("createApp", () => {
     server.close()
   })
 
-  it("should reject errors", async () => {
+  it("should reject errors that happen before the server can listen", async () => {
+    // We listen on an invalid port
+    // causing the app to reject the Promise called at startup
     const port = 2
     const defaultArgs = await setDefaults({
       port,