BAEL-1863 - Calling Callbacks with Mockito (#4531)

* BAEL-1849 - Convert from String to Date in Java

* BAEL-1863 - Calling Callbacks with Mockito

testing-modules/mockito/src/main/java/org/baeldung/mockito/service/ActionHandler.java

@@ -0,0 +1,26 @@
+package org.baeldung.mockito.service;
+
+public class ActionHandler {
+
+    private Service service;
+
+    public ActionHandler(Service service) {
+        this.service = service;
+    }
+
+    public void doAction() {
+        service.doAction("our-request", new Callback<Response>() {
+            @Override
+            public void reply(Response response) {
+                handleResponse(response);
+            }
+        });
+    }
+
+    private void handleResponse(Response response) {
+        if (response.isValid()) {
+            response.setData(new Data("Successful data response"));
+        }
+    }
+
+}

testing-modules/mockito/src/main/java/org/baeldung/mockito/service/Callback.java

@@ -0,0 +1,6 @@
+package org.baeldung.mockito.service;
+
+public interface Callback<T> {
+
+    void reply(T response);
+}

testing-modules/mockito/src/main/java/org/baeldung/mockito/service/Data.java

@@ -0,0 +1,15 @@
+package org.baeldung.mockito.service;
+
+public class Data {
+
+    private String message;
+
+    public Data(String message) {
+        this.message = message;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+}

testing-modules/mockito/src/main/java/org/baeldung/mockito/service/Response.java

@@ -0,0 +1,24 @@
+package org.baeldung.mockito.service;
+
+public class Response {
+
+    private Data data;
+    private boolean isValid = true;
+
+    public boolean isValid() {
+        return isValid;
+    }
+
+    public void setIsValid(boolean isValid) {
+        this.isValid = isValid;
+    }
+
+    public void setData(Data data) {
+        this.data = data;
+    }
+
+    public Data getData() {
+        return data;
+    }
+
+}

testing-modules/mockito/src/main/java/org/baeldung/mockito/service/Service.java

@@ -0,0 +1,7 @@
+package org.baeldung.mockito.service;
+
+public interface Service {
+
+    void doAction(String request, Callback<Response> callback);
+
+}

testing-modules/mockito/src/test/java/org/baeldung/mockito/service/ActionHandlerUnitTest.java

@@ -0,0 +1,65 @@
+package org.baeldung.mockito.service;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.verify;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Captor;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.mockito.stubbing.Answer;
+
+public class ActionHandlerUnitTest {
+
+    @Mock
+    private Service service;
+
+    @Captor
+    private ArgumentCaptor<Callback<Response>> callbackCaptor;
+
+    @Before
+    public void setup() {
+        MockitoAnnotations.initMocks(this);
+    }
+
+    @Test
+    public void givenServiceWithValidResponse_whenCallbackReceived_thenProcessed() {
+        ActionHandler handler = new ActionHandler(service);
+        handler.doAction();
+
+        verify(service).doAction(anyString(), callbackCaptor.capture());
+
+        Callback<Response> callback = callbackCaptor.getValue();
+        Response response = new Response();
+        callback.reply(response);
+
+        String expectedMessage = "Successful data response";
+        Data data = response.getData();
+        assertEquals("Should receive a successful message: ", expectedMessage, data.getMessage());
+    }
+
+    @Test
+    public void givenServiceWithInvalidResponse_whenCallbackReceived_thenNotProcessed() {
+        Response response = new Response();
+        response.setIsValid(false);
+
+        doAnswer((Answer<Void>) invocation -> {
+            Callback<Response> callback = invocation.getArgument(1);
+            callback.reply(response);
+
+            Data data = response.getData();
+            assertNull("No data in invalid response: ", data);
+            return null;
+        }).when(service)
+            .doAction(anyString(), any(Callback.class));
+
+        ActionHandler handler = new ActionHandler(service);
+        handler.doAction();
+    }
+}