Junit - Spring boot: @Value is always null while testing

Question

There is a @Value annotated constant, which is not getting initialized when running test, it throws NullPointerException when it is required inside constructor.

Sample Class to be tested:

class TestClass {
    @Value("${test.value1}")
    private String value1;

    private final TestTemplate testTemplate;

    public TestClass(TestTemplateBuilder builder) {
        testTemplate = builder.someMethod(value1).build();
    }


    ---
}

Sample Test Class:

@RunWith(SpringRunner.class)
@ContextConfiguration(classes = TestClass.class)
@SpringBootTest
class TestClassTest {

    @MockBean
    TestTemplateBuilder builder;

    @Autowired
    TestClass testClass = new TestClass(testTemplate);

    @Before
    public void setUp() {
        ReflectionTestUtils.setField(testClass, "value1", "VALUE");

        Mockito.when(builder.build()).thenReturn(new TestTemplate());
    }

    ---
}

Things tried, but nothing worked:

• I have created application.properties file with required value.
• Created application-test.properties and added @TestPropertySource(locations="classpath:application-test.properties") .
• @SpringBootTest(properties = { "test.value1=VALUE" })

I have tried some other things also, but what i got is NullPoiterException at someMethod(value1) .

Versions:

• Java: 1.8
• Springboot: 2.1.17
• Junit: 4.12
• Mockito: 2.23.4

Answer 1

The reason you are getting NullPointerException is that the value injection occurs after the constructor call. To prevent this you can use spring life cycle hooks to initialize your class after the constructor call.

Answer 2

I was not able to solve the main issue, but i fulfilled my requirement like this.

class TestClassTest {

    TestClass testClass;

    @Before
    public void setUp() {
        TestTemplateBuilder builder = Mockito.mock(TestTemplateBuilder.clsss);

        TestTemplateBuilder builder1 = Mockito.mock(TestTemplateBuilder.clsss);

        Mockito.when(builder.someMethod(nullable(String.class))).thenReturn(builder1);

        Mockito.when(builder1.build()).thenReturn(new TestTemplate());

        testClass = new TestClass(builder);
    }

    ---
}

This might not be the correct way of doing.

Answer 3

Just to make sure (because in the question, it's doesn't showed): class TestClass is Spring bean (Component, Service...)?

Edit ( TestClass is Component ):

This is not how Spring bean are created;

If constructor of TestClass require @Value then only Spring will guarantee that before instantiating TestClass the test.value1 value is available. So you can add to the constructor @Value("${test.value1}")String value1 and set the value1 property.

Please read the ways of how Spring inject.

Answer 4

If @Before is not working, then try with @BeforeEach. It worked for me.

`@BeforeEach
public void setUp() {
    ReflectionTestUtils.setField(yourInstanceClass, "fieldName", "fieldValue");
}`