How to mock static factory method using Mockito

Question

Following is my class where I need to mock "resourceManager.getLicenseSources(licenseId)", how this can be achieved?

class LicenseSourceImpl{
-----
ResourceManager resourceManager = ManagerFactory.getInstance(ResourceManager.class);
List<Source> sources = resourceManager.getLicenseSources(licenseId);
-----
}

Few things I've tried:

1. Mock ManagerFactory itself

   ManagerFactory mf = Mockito.mock(ManagerFactory.class); Mockito.when(mf.getInstance(any())).thenReturn(resourceManager); Mockito.when(resourceManager.getLicenseSources(LICENSE_ID)).thenReturn(sources);

This fails with java.lang.NullPointerException: Cannot invoke "java.lang.Class.getName()" because "clazz" is null

2. Mock ManagerFactory and static mock

   ManagerFactory mf = Mockito.mock(ManagerFactory.class); Mockito.when(mf.getInstance(ResourceManager.class)).thenReturn(resourceManager); Mockito.when(resourceManager.getLicenseSources(LICENSE_ID)).thenReturn(sources);

This fails with

org.mockito.exceptions.misusing.MissingMethodInvocationException: 
when() requires an argument which has to be 'a method call on a mock'.
For example:
    when(mock.getArticles()).thenReturn(articles);

3. Spy on factory static method ResourceManager resourceManager = spy(ManagerFactory.getInstance(ResourceManager.class)); but this not mocking the factory instance and creates a new instance always

Is there a way to mock for these situations?

Answer 1

You would have to use Mockito.mockStatic to mock a static method. See Mockito javadoc on how to do it. But better design would be to avoid accessing the static factory in your class but rather have the ResourceManager injected, so that you can inject a regular mock in your test...

Answer 2

You can follow this link to see how you can mock a static method https://www.baeldung.com/mockito-mock-static-methods

You can use

try (MockedStatic<ResourceManager> resourceManagerMock = Mockito.mockStatic(ResourceManager.class)) {
}