Unable to mock Mono object - spring-boot

Question

I have been writing unit tests for Spring reactive app. I am trying to stub method response which returns Mono. I tried with samples on the net. But it is giving Null pointer exception. If we can't stub Mono types with Mockito , Please suggest me alternative way.
Complete code is available in below repository
https://github.com/NarayanaBojja/example-service
public Mono<Person> getName() {
Mono<Person> nameMono = name();
return nameMono.flatMap(per -> Mono.just(per)).onErrorResume(error -> {
return Mono.error(new RuntimeException("Name not found"));
});
}
public Mono<Person> name() {
Person person = new Person();
person.setName("Narayana");
return Mono.just(person);
}
Unit test case for the above code is
#RunWith(SpringRunner.class)
#SpringBootTest
public class DemoApplicationTests {
#Autowired
private ExampleService exampleService;
#Test
public void getNameTest() {
Person person = new Person();
person.setName("Narayana");
Mono<Person> nameMono = Mono.just(person);
given(this.exampleService.name()).willReturn(nameMono);
StepVerifier.create(exampleService.getName()).expectNext(person).verifyComplete();
}
}
I am getting below Exception
java.lang.NullPointerException
at reactor.test.DefaultStepVerifierBuilder$DefaultStepVerifier.verify(DefaultStepVerifierBuilder.java:801)
at reactor.test.DefaultStepVerifierBuilder$DefaultStepVerifier.verify(DefaultStepVerifierBuilder.java:772)
at reactor.test.DefaultStepVerifierBuilder.verifyComplete(DefaultStepVerifierBuilder.java:644)
at com.example.demo.DemoApplicationTests.getNameTest(DemoApplicationTests.java:29)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74)
at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84)
at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)