isEmpty() on an ArrayList results in false although its size is 0

Question

In a test I inject a mock to another class which seems to work properly. However, when I check the ArrayList if it is empty the result is false although its length/size is 0. How can this happen and how can I solve this problem?

@Slf4j
@Configuration
@RequiredArgsConstructor
@Setter(onMethod_ = @SuppressFBWarnings({"EI_EXPOSE_REP2", "EI_EXPOSE_REP"}))
@Getter(onMethod_ = @SuppressFBWarnings({"EI_EXPOSE_REP2", "EI_EXPOSE_REP"}))
@EnableConfigurationProperties(MyProperties.class)
public class MyConfig {

    private final MyProperties myProperties;

    private final GenericApplicationContext applicationContext;

    @PostConstruct
    void init() {
        Objects.requireNonNull(myProperties, "myProperties needs not to be null.");
        if (/*myProperties.getApps().size() == 0 || */myProperties.getApps().isEmpty()) {
            log.info("bla bla bla");
        } else {
            ...
        }
    }
}

Here's my test class:

@ExtendWith(MockitoExtension.class)
class MyConfigTest {

    @Mock
    MyProperties myPropertiesMock;

    @InjectMocks
    MyConfig myConfig;

    ApplicationContextRunner contextRunner;

    @Test
    void should_check_for_empty_apps() {
        contextRunner = new ApplicationContextRunner()
            .withPropertyValues("foobar.apps[0].name=", "foobar.apps[0].baseUrl=", "foobar.apps[0].basePath=")
        ;

        List apps = Mockito.mock(ArrayList.class);
        when(myPropertiesMock.getApps()).thenReturn(apps);

        myConfig.init();

        contextRunner.run(context -> {
            assertThat(apps.size()).isEqualTo(0);
        });
    }
}

The properties class:

@Slf4j
@Validated
@Data
@Setter(onMethod_ = @SuppressFBWarnings({"EI_EXPOSE_REP2", "EI_EXPOSE_REP"}))
@Getter(onMethod_ = @SuppressFBWarnings({"EI_EXPOSE_REP2", "EI_EXPOSE_REP"}))
@ConfigurationProperties(prefix = MyProperties.CONFIG_PREFIX)
public class MyProperties implements LoggableProperties {

    public static final String CONFIG_PREFIX = "foobar";

    @Valid
    @NestedConfigurationProperty
    private List<MyEndpoint> apps = new ArrayList<>();

    @Data
    public static class MyEndpoint {
//        @NotNull
//        @NotEmpty
        private String baseUrl = "";

        private String basePath = "";

//        @NotNull
//        @NotEmpty
        private String name = "";
    }
}

Answer 1

‘app’ is a mock. You have to mock any method that you use, otherwise it retrieve type’s default value.