BAEL-7002 - Drawbacks of Singleton Pattern (#14979)

* BAEL-7002 - Drawbacks of Singleton Pattern

* Add mockito-inline dependency

patterns-modules/design-patterns-creational-2/src/test/java/com/baeldung/singleton/SingletonUnitTest.java

@@ -0,0 +1,35 @@
+package com.baeldung.singleton;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.mockito.MockedStatic;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockStatic;
+
+class SingletonUnitTest {
+
+    @Test
+    void givenTwoValues_whenSum_thenReturnCorrectResult() {
+        SingletonDemo singletonDemo = new SingletonDemo();
+        int result = singletonDemo.sum(12, 4);
+        Assertions.assertEquals(16, result);
+    }
+
+    @Test
+    void givenMockedLogger_whenSum_thenReturnCorrectResult() {
+        Logger logger = mock(Logger.class);
+
+        try (MockedStatic<Logger> loggerMockedStatic = mockStatic(Logger.class)) {
+            loggerMockedStatic.when(Logger::getInstance).thenReturn(logger);
+            doNothing().when(logger).log(any());
+
+            SingletonDemo singletonDemo = new SingletonDemo();
+            int result = singletonDemo.sum(12, 4);
+            Assertions.assertEquals(16, result);
+        }
+    }
+
+}