PowerMockito -- Mock and Spy

A bad system design can lead to much hard work. In order to increase the unit tests coverage, I recently started to work on writing unit tests for some classes. One of the case is I want to test a method as follow:

public final ReturnType getMethod (SomeRequest someRequest) {
    AnotherRequest anotherRequest = new AnotherRequest(someRequest);
    SomeResponse someResponse = SomeService.getInstance().someMethod(anotherRequest);
    SomeValue someValue = someResponse.getValue();
    /**
     * Some processes with someValue..
     */
}

The main purpose of this test is testing the process with someValue, so I should just mock the .getValue() method. But the thing is not that easy. Let me put more related classes here:
SomeService.class

public final class SomeService {
    private static SomeService instance = new SomeService();
    static {
        // A static block
    }
    protected SomeService() {}
    public static SomeService getInstance() {
        return instance;
    }
    public SomeResponse someMethod(AnotherRequest anotherRequest) {
        // Implementation of the method..
    }
}

SomeResponse.class

public class SomeResponse {
    public SomeValue getValue() {
        // Implementation of getValue()
    }
}

SomeValue.class

public class SomeValue {
    private String name;
    private void populateValue(PreDefinedType preDefinedType) {
        // Generate name from a preDefinedType, basically a black box.
    }
    public String getName() {
        return name;
    }
}

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