BAEL-5777 - Mocking a singleton with Mockito (#12977)

* BAEL-5777 - Mocking a singleton with Mockito

* BAEL-5777 - Mocking a singleton with Mockito - changing test class name

* BAEL-5777 - Mocking a singleton with Mockito - moving to new module

testing-modules/mockito-2/src/main/java/com/baeldung/singleton/CacheManager.java

@@ -0,0 +1,29 @@
+package com.baeldung.singleton;
+
+import java.util.HashMap;
+
+public class CacheManager {
+    private final HashMap<String, Object> map;
+
+    private static CacheManager instance;
+
+    private CacheManager() {
+        map = new HashMap<>();
+    }
+
+    public static CacheManager getInstance() {
+        if(instance == null) {
+            instance = new CacheManager();
+        }
+
+        return instance;
+    }
+
+    public <T> T getValue(String key, Class<T> clazz) {
+        return clazz.cast(map.get(key));
+    }
+
+    public Object setValue(String key, Object value) {
+        return map.put(key, value);
+    }
+}

testing-modules/mockito-2/src/main/java/com/baeldung/singleton/Product.java

@@ -0,0 +1,27 @@
+package com.baeldung.singleton;
+
+public class Product {
+    private String name;
+    private String description;
+
+    public Product(String name, String description) {
+        this.name = name;
+        this.description = description;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getDescription() {
+        return description;
+    }
+
+    public void setDescription(String description) {
+        this.description = description;
+    }
+}

testing-modules/mockito-2/src/main/java/com/baeldung/singleton/ProductDAO.java

@@ -0,0 +1,8 @@
+package com.baeldung.singleton;
+
+public class ProductDAO {
+    public Product getProduct(String productName) {
+
+        return new Product(productName, "description");
+    }
+}

testing-modules/mockito-2/src/main/java/com/baeldung/singleton/ProductService.java

@@ -0,0 +1,26 @@
+package com.baeldung.singleton;
+
+public class ProductService {
+
+    private final ProductDAO productDAO;
+    private final CacheManager cacheManager;
+
+    public ProductService(ProductDAO productDAO) {
+        this.productDAO = productDAO;
+        this.cacheManager = CacheManager.getInstance();
+    }
+
+    public ProductService(ProductDAO productDAO, CacheManager cacheManager) {
+        this.productDAO = productDAO;
+        this.cacheManager = cacheManager;
+    }
+
+    public Product getProduct(String productName) {
+        Product product = cacheManager.getValue(productName, Product.class);
+        if (product == null) {
+            product = productDAO.getProduct(productName);
+        }
+
+        return product;
+    }
+}

testing-modules/mockito-2/src/test/java/com/baeldung/singleton/ProductServiceTest.java

@@ -0,0 +1,40 @@
+package com.baeldung.singleton;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.MockedStatic;
+import org.mockito.Mockito;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.*;
+
+class ProductServiceUnitTest {
+
+    @Test
+    void givenValueExistsInCache_whenGetProduct_thenDAOIsNotCalled() {
+        ProductDAO productDAO = mock(ProductDAO.class);
+        CacheManager cacheManager = mock(CacheManager.class);
+        Product product = new Product("product1", "description");
+        ProductService productService = new ProductService(productDAO, cacheManager);
+
+        when(cacheManager.getValue(any(), any())).thenReturn(product);
+
+        productService.getProduct("product1");
+
+        Mockito.verify(productDAO, times(0)).getProduct(any());
+    }
+
+    @Test
+    void givenValueExistsInCache_whenGetProduct_thenDAOIsNotCalled_mockingStatic() {
+        ProductDAO productDAO = mock(ProductDAO.class);
+        CacheManager cacheManager = mock(CacheManager.class);
+        Product product = new Product("product1", "description");
+
+        try (MockedStatic<CacheManager> cacheManagerMock = mockStatic(CacheManager.class)) {
+            cacheManagerMock.when(CacheManager::getInstance).thenReturn(cacheManager);
+            when(cacheManager.getValue(any(), any())).thenReturn(product);
+            ProductService productService = new ProductService(productDAO);
+            productService.getProduct("product1");
+            Mockito.verify(productDAO, times(0)).getProduct(any());
+        }
+    }
+}

testing-modules/mockito-2/src/test/resources/mockito-extensions/org.mockito.plugins.MockMaker

@@ -0,0 +1 @@
+mock-maker-inline