Junit test class for dependency with value from application.properties

Question

I am writing Junit test case for the following class :

@Component public class ExpandParam { /* expand parameter with value "expand" */ @Value("${api.expand.value}") private String expandParam; public MultiValueMap<String, String> getExpandQueryParam(String[] expand) { MultiValueMap<String, String> queryParams = new LinkedMultiValueMap<>(); // Creating comma separated format string StringBuilder builder = new StringBuilder(); for (String value : expand) { if(!expand[expand.length-1].equals(value)) { builder.append(value+", "); } else { builder.append(value); } } String expandText = builder.toString(); queryParams.add(expandParam, expandText); return queryParams; } }

The test class is following :

public class ExpandParamTest { @InjectMocks @Spy ExpandParam expandQueryParam; // @Value("${api.expand.value}") // private String expandParam; private String[] expand = {"fees"}; @Before public void setup() { ReflectionTestUtils.setField(expandQueryParam, "expandParam", "expand"); } @Test public void testExpandParam() { MultiValueMap<String, String> queryParams = expandQueryParam.getExpandQueryParam(expand); try { System.out.println(new ObjectMapper().writeValueAsString(queryParams)); } catch (JsonProcessingException e) { // TODO Auto-generated catch block e.printStackTrace(); } } }

In application. properties files I have set the values :

#expand param api.expand.value: expand

I am new to this, can any one tell me where I am making the mistake: Getting the following error:

java.lang.IllegalArgumentException: Either targetObject or targetClass for the field must be specified at org.springframework.util.Assert.isTrue(Assert.java:121) at org.springframework.test.util.ReflectionTestUtils.setField(ReflectionTestUtils.java:178) at org.springframework.test.util.ReflectionTestUtils.setField(ReflectionTestUtils.java:107) at org.springframework.test.util.ReflectionTestUtils.setField(ReflectionTestUtils.java:91) at com.aig.rs.products.orchestrator.api.utils.ExpandParamTest.setup(ExpandParamTest.java:29)

Looks like expandQueryParam is null. Try creating it in setup. — tgdavies
– tgdavies, Commented Jul 12, 2021 at 6:47

Yayotrón · Accepted Answer · 2021-07-12 09:07:20Z

@Value is a spring annotation, it depends on the Spring Context to function. If you want @Value to read the value from your application properties then you need to convert your unit test into a @SpringBootTest. Take a look at this tutorial to understand a bit more about Spring Test.

You're also using ReflectionTestUtils.setField(expandQueryParam, "expandParam", "expand"); which will just set a value to this field, not read it from properties. This exception you're seeing is because expandQueryParam is null, these annotations @Spy and @InjectMocks are Mockito annotations and for them to initialize your object you need to enable mockito annotations, you can do this by adding @ExtendWith(MockitoExtension.class) on top of your class or using MockitoAnnotations.initMocks(this) in setUp method.

I don't think you need mockito to test this class, in my opinion going for a Spring Test would be a better option this way you can also test the reading of the property key.

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