Practical Test Code Writing Know-How Part 2: Using Feedback Through Test Code

Test code goes beyond simply being a tool for verifying logic—it serves as the first user of implementation code. By reflecting the feedback that test code provides, you can improve implementation code into a more concise and easily verifiable structure, creating a virtuous cycle of writing better code.

An object's Responsibility is a key element in responding to change. If a PartnerClient object holds both HTTP communication and business logic responsibilities, then whenever the API specification changes or the business logic is modified, the scope of code impact widens, making maintenance difficult.

Code whose responsibilities are not properly separated gives the following feedback during the testing process:

• An increase in the amount of unnecessary test code that obscures the Main Concern (e.g., excessive involvement with HTTP methods or response bodies)
• A structure where it is difficult to verify core logic such as Deserialization

Based on this feedback, PartnerClient can be refactored to be solely responsible for HTTP communication, improving it into a structure that can flexibly respond to change.