Implement Flask Routes for Product Management

[JiayangYing]

Description

We need to implement two Flask routes for our product management system:

1. @app.route('/product') - This route will return information about all products in our database or data structure. It should provide a JSON response listing all products.
2. @app.route('/product/') - This route will return details of a specific product identified by product_id. If the product exists, it should return the product's details in JSON format. If the product does not exist, it should return a 404 Not Found error.

Requirements

1. Implement the Flask routes as described.
2. Ensure the routes handle errors gracefully, especially for non-existent product IDs.

Expected Behavior

1. /product: Should list all products.
2. /product/: Should return the details of the product if found, or a 404 error if not found.

Additional Notes

1. Please consider scalability and potential future integration with a real database.
2. Include basic unit tests to verify the routes' functionality.

[JiayangYing]

closed #59