Junit java actual called method is returning null value

Question

This is an Utility class with final and private constructor all methods in this class are static.

When called the methods for testing they returned null value always.

Kindly Help.

` public final class ImageUtil {
final static Logger logger = LoggerFactory.getLogger(ImageUtil.class);

private ImageUtil() {}

private static final int MAX_MASTER_WIDTH = 2000;
private static final int MIN_MASTER_WIDTH = 500;
private static final int MAX_SAMPLE_WIDTH = 400;

public static BufferedImage scaleImage(BufferedImage image, int maxWidth, int type){
    int oldWidth = image.getWidth();
    int oldHeight = image.getHeight();
    int newHeight = (int) Math.round((double) maxWidth / (double) oldWidth * (double) oldHeight);

    BufferedImage resized = new BufferedImage(maxWidth, newHeight, type);
    Graphics2D g = resized.createGraphics();
    g.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
    g.drawImage(image, 0, 0, maxWidth, newHeight, 0, 0, image.getWidth(), image.getHeight(), null);
    g.dispose();

    return resized;
}}`

TestClass Code

@PrepareForTest(value = {FileUtil.class,JpegReader.class,ImageUtil.class,System.class,FileUtils.class,JpegReader.class,ImageIO.class})
@ExtendWith(MockitoExtension.class)
@MockitoSettings(strictness = Strictness.LENIENT)

class ImageUtilTest {

    MockedStatic<ImageUtil> imageUtil= null ;
    File tempFile = null;

    @ClassRule
    TemporaryFolder temporaryFolder ;
    
     @BeforeEach
      public void init() throws IOException {
         imageUtil= mockStatic(ImageUtil.class);
         tempFile = mock(File.class);
         temporaryFolder = new TemporaryFolder();
         temporaryFolder.create();
      }

      @AfterEach
      public void afterEach() {
          imageUtil.close();
          tempFile.delete();
          temporaryFolder.delete();
      }
      
      @Test
      @DisplayName("scaleImageTest")
      public  void scaleImageTest() throws Exception{
          int oldWidth = 200;
          int oldHeight = 150;
          int newHeight = (int) Math.round((double) 200 / (double) oldWidth * (double) oldHeight);

          BufferedImage mockedImage = mock(BufferedImage.class) ;
          BufferedImage mockedNewImage = mock(BufferedImage.class) ;
          Graphics2D mockedGraphics = mock(Graphics2D.class);
          
          when(mockedImage.getWidth()).thenReturn(oldWidth);
          when(mockedImage.getHeight()).thenReturn(oldHeight);
          when(mockedImage.getWidth()).thenReturn(200);
          
          Mockito.doNothing().when(mockedGraphics).setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
          when(mockedGraphics.drawImage(mockedImage, 0, 0, 200, newHeight, 0, 0, oldHeight,oldWidth, null)).thenReturn(true);
          Mockito.doNothing().when(mockedGraphics).dispose();

          PowerMockito.whenNew(BufferedImage.class).withArguments(oldWidth, oldHeight,newHeight).thenReturn(mockedNewImage);
          when(mockedNewImage.createGraphics()).thenReturn(mockedGraphics);
          
          BufferedImage actualImage = ImageUtil.scaleImage(mockedImage, oldWidth, newHeight);
          assertEquals(mockedNewImage, actualImage);
          
      }

Stacktrace

org.opentest4j.AssertionFailedError: expected: <Mock for BufferedImage, hashCode: 307036850> but was: <null>
    at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:55)
    at org.junit.jupiter.api.AssertionUtils.failNotEqual(AssertionUtils.java:62)
    at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:182)
    at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
    at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1141)
    at test.com.renoworks.framework.util.ImageUtilTest.scaleImageTest(ImageUtilTest.java:234)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:725)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
    at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
    at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$7(TestMethodTestDescriptor.java:214)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:210)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:66)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:151)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)

BufferedImage actualImage = ImageUtil.scaleImage(mockedImage, oldWidth, newHeight);

This should work properly and should return some real data, but its not working . Please help me . Above code of line giving me always null value. Thanks in advance.

Answer 1

I have got the answer: I am doing unnecessary mocking even in real method its actually creating objects. This is the working code:

  @Test
  public  void scaleImageTest() throws Exception{
        // Setup
      int oldWidth = 200;
      int oldHeight = 150;
      BufferedImage buffImage = new BufferedImage(oldWidth, oldHeight, 1);
      //  imageUtil this variable is mockedStatic
      imageUtil.when(()->ImageUtil.scaleImage(buffImage, oldWidth, 1)).thenCallRealMethod();
      // Run the test
      BufferedImage actualImage = ImageUtil.scaleImage(buffImage, oldWidth, 1);
        // Verify the results
      assertNotNull( actualImage);
      
  }