@Autowired Junit 中的注入依赖项测试始终为 null

Question

In a simple test class like the one below:

@SpringBootTest
@Slf4j
@ActiveProfiles("test")
public class LocalizerTest {

    @Autowired
    AddressInfoLocalizer addressInfoLocalizer;


    @Test
    public void localizeIp() {
        String ip = "8.8.8.8";
        Optional<CityResponse> response = addressInfoLocalizer.localize(ip);
        response.ifPresent(cityResponse -> log.info("{}", cityResponse));
    }

}

With the AddressInfoLocalizer (sorry for the strange name but I had to make it up) being basically like this:

@Slf4j
@Component
public class AddressInfoLocalizer {

    @Value("${geolocalization.dbpath}")
    private String databasePath;

    private DatabaseReader database;

    @PostConstruct
    public void initialize() {
        log.info("GeoIP2 database path:{}", databasePath);
        File database = new File(databasePath);
        try {
            this.database = new DatabaseReader.Builder(database).build();
        } catch (IOException ioe) {
            this.database = null;
            log.warn("Problems encountered while initializing IP localization database, skipping resolutions");
        }

    }

    public Optional<CityResponse> localize(String ipAddressString) {
        if (isNull(database)) {
            log.warn("Attempted to resolve an IP location with database problems, skipping.");
            return Optional.empty();
        }
        try {
            InetAddress ipAddress = InetAddress.getByName(ipAddressString);
            return ofNullable(database.city(ipAddress));
        } catch (UnknownHostException uhe) {
            log.error("Unknown host {}, {}", ipAddressString, uhe.getCause());
            return Optional.empty();
        } catch (IOException ioe) {
            log.error("IO error while opening database, {}", ioe.getCause().toString());
            return Optional.empty();
        } catch (GeoIp2Exception gip2e) {
            log.error("GeoIP error, {}", gip2e.getCause().toString());
            return Optional.empty();
        }
    }
}

I keep getting a NullPointerException when calling (in the test) addressInfoLocalizer.localize(ip); ,

java.lang.NullPointerException
    at com.bok.parent.LocalizerTest.localizeIp(LocalizerTest.java:26)
    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: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.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.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:221)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)

while debugging I can actually see that the addressInfoLocalizer object is null .

I've created other classes the same way, but only this one seems to have that problem, what could be wrong?

Answer 1

What I found out is that not always the @SpringBootTest is enough, in some classes/cases (to be honest I don't have a 100% clear idea so I'm not gonna say stupidities) it is needed that you manually choose the test-runner, like below:

@SpringBootTest
@RunWith(SpringRunner.class)
public class FooTest {
...
}

Keep in mind that if you decide to instantiate a dependency by yourself then Spring won't be able to inject all the needed classes, and then you'd need to change the runner into something like @RunWith(MockitoJUnitRunner.class)

(credits to JUNIT Autowired instance is always null )

Answer 2

Better approach is to use spring's underlying mock beans.

@SpringBootTest(classes= AddressInfoLocalizer.class)

this is actually the new recommended way.

Answer 3

Two things here:

1. If you're testing, the ideal way is to mock instead of autowire(there can be exceptions)
   
2. You should use @ExtendWith(MockitoExtension.class) or @RunWith(MockitoJUnitRunner.class) so that your components will be loaded in spring context. However ExtendWith is preferred way to initialize beans/components. Because the later(RunWith) loads the entire spring context which might take more time

So, your code should look something like:

@Slf4j
@ActiveProfiles("test")
@ExtendWith(MockitoExtension.class)
public class LocalizerTest {

    @Mock
    AddressInfoLocalizer addressInfoLocalizer;


    @Test
    public void localizeIp() {
        String ip = "8.8.8.8";
         //Mock here.
        Optional<CityResponse> response = addressInfoLocalizer.localize(ip);
        response.ifPresent(cityResponse -> log.info("{}", cityResponse));
    }

}

Reference/Read more:
https://www.baeldung.com/mockito-junit-5-extension
https://stackoverflow.com/questions/55276555/when-to-use-runwith-and-when-extendwith
https://www.javadoc.io/static/org.mockito/mockito-junit-jupiter/3.10.0/org/mockito/junit/jupiter/MockitoExtension.html