Designing classes to help Junit Testing

Question

I will try to explain through pseudocode a code quality or design issue that I encountered while testing a spring boot application:

public class ControllerClass {
    controllerMethod(@RequestParam(version) String version) {

        service.generateFile(version)

    }
}

public class ServiceClass {

    private map = new HashMap<> ();

    void generateFile(version) {
        String rVersion = fetchRversion(version);
        String json = makeApiCall(url + rVersion);
        build(map);
        generateData(json)

    }
    generateData(json) {
        // uses map
    }
}

The above way of coding cause trouble when testing the generateData method. So if I have the JSON, I pass it to the generateData function. The trouble will be that map is built inside the generateFile function.
So it won't work. Either I built the map inside the test function for generateData or there could be some way of creating the Service class object with the map so that no testing function has to care about building or instantiating any other data. Since the version is passed at run time and based on that the map is built, will it be appropriate to have a separate build function inside the service class which can be called to setup all the required things?
Any alternative to this approach?

Answer 1

If I understand the issue correctly, it looks like a case of sequential coupling. Consider a modified design of the class.

The simplest option is to add the required map as a method parameter to the generateData method:

generateData(json, map) {
    // uses map
}