Spy on java object throws exception

Question

I have written a simple java class and using the Mockito framework I am trying to create a spy on the object. But whenever I try to run the test the test throws an Exception. Any idea what I am doing wrong ? My ultimate goal is to override getSession() and provide my own fake version of Session.

The class is,

public class FetchJob  extends Executor {
    public Session getSession() { ... }
    
    @Override
    public void execute(ApplicationArguments args) { ... }
      
 }


public class FetchJobTest {
  @Before
  public void setup() {}

  @Test
  public void testFetch() throws {
    FetchJob job = new FetchJob();
    FetchJob spy = spy(job);  // This line thorws exception
  }

}

The error I am getting is,

java.lang.ExceptionInInitializerError
    at org.mockito.cglib.core.KeyFactory$Generator.generateClass(KeyFactory.java:167)
    at org.mockito.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25)
    at org.mockito.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:217)
    at org.mockito.cglib.core.KeyFactory$Generator.create(KeyFactory.java:145)
    at org.mockito.cglib.core.KeyFactory.create(KeyFactory.java:117)
    at org.mockito.cglib.core.KeyFactory.create(KeyFactory.java:109)
    at org.mockito.cglib.core.KeyFactory.create(KeyFactory.java:105)
    at org.mockito.cglib.proxy.Enhancer.<clinit>(Enhancer.java:70)
    at org.mockito.internal.creation.cglib.ClassImposterizer.createProxyClass(ClassImposterizer.java:95)
    at org.mockito.internal.creation.cglib.ClassImposterizer.imposterise(ClassImposterizer.java:57)
    at org.mockito.internal.creation.cglib.ClassImposterizer.imposterise(ClassImposterizer.java:49)
    at org.mockito.internal.creation.cglib.CglibMockMaker.createMock(CglibMockMaker.java:24)
    at org.mockito.internal.util.MockUtil.createMock(MockUtil.java:33)
    at org.mockito.internal.MockitoCore.mock(MockitoCore.java:59)
    at org.mockito.Mockito.spy(Mockito.java:1368)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
    at java.base/java.lang.reflect.Method.invoke(Method.java:577)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
    at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
    at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
    at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @707f7052
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:354)
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
    at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:200)
    at java.base/java.lang.reflect.Method.setAccessible(Method.java:194)
    at org.mockito.cglib.core.ReflectUtils$2.run(ReflectUtils.java:57)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:318)
    at org.mockito.cglib.core.ReflectUtils.<clinit>(ReflectUtils.java:47)
    ... 42 more