Spring Autowire bean NullPointerException during Groovy tests but works fine during Runtime - spring-boot

Question

I am using the prometheus library for getting metrics of my Spring Boot application (REST API). I am using the library io.prometheus.simpleclient:0.4.0 and I am including it in my Maven pom.xml. I am using the Counter and #Autowiring (I've tried both field and constructor injection) it to one of my own classes, like such
MyCustomMetricsClass.java
#Component
public MyCustomMetricsClass {
#Autowire
private Counter counterBean;
public void myOwnMetricsMethod() {
counterBean.inc();
// do some stuff
}
THEN, I am #Autowiring this MyCustomMetricsClass into my Service class, MyServiceClass.java, where it seems to run fine when I run my API locally using Spring Boot embedded tomcat on port 8080 (localhost:8080). I can hit endpoints and the metrics are being reported correctly at the actuator endpoint (localhost:8080/actuator/metrics). e.g.
MyServiceClass.java
public MyServiceClass {
#Autowire
private MyCustomMetricsclass myMetrics;
public void genericServiceMethod() {
myMetrics.MyOwnMetricsMethod(); // NULL POINTER EXCEPTION ONLY DURING TEST SCOPE (GROOVY)
}
The problem is, when I run mvn install, which triggers the local Groovy unit tests I have written, I keep getting a NULL POINTER EXCEPTION. With the debugger, I can debug the Groovy unit tests and see in my Service class, the myMetrics variable is NULL. But I don't understand why it works fine at runtime, also, I have annotated the MyCustomMetricsClass as a #Component annotation, so it should be a bean being scanned by Spring Component scan.
This is a multi-module project ; with the structure below
my-project (root, contains root pom.xml)
- my-api (module, contains RestController. has its own pom.xml)
- my-service (module. contains service classes, has its own pom.xml)
- my-model (module, contains all POJO/DTO model classes, has its own pom.xml)
Am I missing some dependency on my classpath? Why does it work at runtime but not during tests? (all my dependencies should have default scope) Is the autowiring broken?

Answer 1

Can you share the code from your unit test?
At a guess, you're using a mocking framework, maybe Mockito?
If this assumption is true, remember, your unit test won't be running up the full Spring context, so no auto-wiring will take place. You will need to inject mocks for the autowired components.
e.g.:
#RunWith(MockitoJUnitRunner.class)
public class MyServiceClassTest {
#Mock
private MyCustomMetricsClass myCustomMetricsClass;
#InjectMocks
private MyServiceClass myServiceClass;
#Test
public void shouldDoTesting() {
myServiceClass. genericServiceMethod();
verify(myMetrics).MyOwnMetricsMethod();
}
}