Is there away to mock UUID in Mockito without using powermock?

Question

I want to mock an object that has a uuid value but I don't want to install powermock.

Answer 1

Your easiest way to achieve this will be to wrap up your UUID generation.

Suppose you have a class using UUID.randomUUID

public Clazz MyClazz{

public void doSomething(){
    UUID uuid = UUID.randomUUID();
}

}

The UUID geneartion is completely tied to the JDK implementation. A solution would to be wrap the UUID generation that could be replaced at test time with a different dependency.

Spring has an interface for this exact senario, https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/util/IdGenerator.html

I'm not suggesting you use Spring for this interface just informational purposes.

You can then wrap up your UUID generation,

public class MyClazz{

private final idGeneartor;

public MyClazz(IdGeneartor idGenerator){
    this.idGenerator = idGenerator;
}

public void doSomething(){
    UUID uuid =idGenerator.generateId();
}

You can then have multiple implementations of UUID geneartion depending on your needs

public JDKIdGeneartor implements IdGenerator(){

    public UUID generateId(){
       return UUID.randomUUID();
    }
}

And a hardcoded impl that will always return the same UUID.

public HardCodedIdGenerator implements IdGenerator(){

    public UUID generateId(){
       return UUID.nameUUIDFromBytes("hardcoded".getBytes());
    }
}

At test time you can construct your object with the HardCodedIdGeneartor allowing you to know what the generated ID will be and assert more freely.