Refactor tests for expense submission endpoints

[mykhalenych]

No description provided.

[mateacademy-ai-mentor]

Review Summary

I am requesting changes because the HTTP server implementation is incomplete/broken, which prevents the tests from running successfully and blocks the task’s core functionality.

Critical issues that must be fixed:

1. In src/createServer.js (around the export at the bottom of the file, e.g. lines 10–20), createServer() is currently returning undefined, so the tests fail with TypeError: Cannot read properties of undefined (reading 'listen'); you need to import http, call http.createServer(app) (where app is your request handler), and return that Server instance, then export createServer in the way the tests import it.
2. The request handler (likely in src/app.js, around the main http.createServer callback or exported function) must implement the required routes: GET / should respond with status 200, Content-Type: text/html, and an HTML form that includes inputs named date, title, and amount; POST /add-expense must parse both application/x-www-form-urlencoded and application/json bodies, validate that all three fields are present, write valid JSON data to db/expense.json only when the input is valid, and send back an HTML page containing formatted JSON (e.g. JSON.stringify(data, null, 2) inside <pre>); any other path must return a 404 status with a non-empty body.
3. For invalid POST requests missing any required field, ensure you respond with status 400 and do not change the existing contents of db/expense.json (the tests pre-populate this file and then check that it remains untouched in error cases), so your validation logic should short‑circuit before any file write.

Minor improvements:

• Make sure you set appropriate headers (especially Content-Type: text/html for HTML responses and a reasonable content type for errors) and keep responses simple but non-empty for 400 and 404 cases.

Once you adjust createServer to return a proper http.Server and implement the route behavior above, your solution should align well with the test expectations, and you’re very close—use the failing test messages as a guide to refine the last details.

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