MeterRegistry counter test case failing-CodePudding

I have implemented micro-meter Prometheus counter in my service by injecting MeterRegistry and incrementing the count as shown below , and I have written a test case as well , but when I am running the test case , I am getting

"java.lang.NullPointerException: Cannot invoke "io.micrometer.core.instrument.MeterRegistry.counter(String, String[])" because "this.meterRegistry" is null".

Please can someone help

Service file:

    @Autowired
    private MeterRegistry meterRegistry;
    
    public void counterIncrement()
    { 
    meterRegistry.counter("test_count").increment();
    }

Test case file:

    @MockBean
    private MeterRegistry registry;
     
    @Test
    void testCounter()
   {
    //  invoking counterIncrement();
    }

CodePudding user response：

Depending on which junit version you are using you need to add the annotation to your test class. Junit 5: @ExtendWith(MockitoExtension.class) or for Junit 4: @RunWith(MockitoJUnitRunner.class)

CodePudding user response：

How do you create your class under test? Since the registry is never instantiated, something seems up with how you setup your test.

Check that you are using the @MockBean in the correct way. This will replace the bean in the application context and if you do not spin up a spring context i your test, it will not work. See this post for more info

A different approach would be to use @Mock and inject the registry in the constructor, example:

@ExtendWith(MockitoExtension.class)
public class MyServiceTest {

  @Mock
  private MeterRegistry registry;

  private MyService myService;

  @BeforeEach
  void setup() {
    myService = new MyService(registry);
  }

  @Test
  void testCounter() {
    var counter = mock(Counter.class);
    given(registry.counter(any(String.class))).willReturn(counter);
    myService.counterIncrement();
  }