Java - How Mock static block with Mockito

Question

Supposed I have legacy ElasticSearchIndexManager that is Singletone with static block as in the picture below that cannot be changed, my goal is create Mock with any framework supported by latest java JDK.

Previously we used PowerMock that did the Job as it had ability to create mockStaticPartial that eliminate static block at the startup of as ElasticSearchIndexManager as in the code below.

PowerMock.mockStaticPartial(ElasticSearchIndexManager.class, "getInstance");
        EasyMock.expect(
                ElasticSearchIndexManager.getInstance(EasyMock.anyObject(AWSRegion.class)))
                .andReturn(null).anyTimes();

The problem that it is PowerMock not supported with higher versions of JDK.

Now I've tried use Mockito 3.7.7 and it helped a bit but not solved my issue cause we have in Legacy code static block. In PowerMock we eliminate it by using mockStaticPartial.

POM.xml

        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>3.7.7</version>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-inline</artifactId>
            <version>3.7.7</version>
            <scope>test</scope>
        </dependency>

// New code - with 3.7.7 Mockito
    @Test
        public void testMockElasticSearchIndexManager() {
            AWSRegion region = mock(AWSRegion.class);
    
            try (MockedStatic<ElasticSearchIndexManager> theMock = Mockito.mockStatic(ElasticSearchIndexManager.class)) {
                theMock.when(() -> ElasticSearchIndexManager.getInstance(region)).thenReturn(null);
            }

        assertEquals(null, ElasticSearchIndexManager.getInstance(region));
    }

Maybe I missed something? I got Exception before assertion org.mockito.exceptions.base.MockitoException: Cannot instrument class com.cloudally.index.ElasticSearchIndexManager because it or one of its supertypes could not be initialized

, If I remove static block it will work, How and is there any same ability to create with Mockito partial static mock, or other ways are welcome

Thanks a lot.

Answer 1

Can you try?

try (MockedStatic<ElasticSearchIndexManager> theMock = Mockito.mockStatic(ElasticSearchIndexManager.class)) {
    theMock.when(() -> ElasticSearchIndexManager.getInstance(region)).thenReturn(null);
    assertEquals(null, ElasticSearchIndexManager.getInstance(region));
}

Mock context is active only inside the try-with-resource block. When it goes outside the scope, it gets closed.