test: migrate to MockitoExtension and clean up test structure

- Replace MockitoAnnotations.openMocks() with @ExtendWith(MockitoExtension.class)
- Remove public modifiers from test classes and methods (package-private)
- Clean up unnecessary imports and mock stubbings
- Ensure proper JUnit 5 + Mockito integration

Author: Gdm0714

powertools-idempotency/powertools-idempotency-dynamodb/src/test/java/software/amazon/lambda/powertools/idempotency/persistence/dynamodb/DynamoDBPersistenceStoreTest.java

@@ -16,9 +16,10 @@
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
 import org.junitpioneer.jupiter.SetEnvironmentVariable;
 import org.mockito.Mock;
-import org.mockito.MockitoAnnotations;
+import org.mockito.junit.jupiter.MockitoExtension;
 
 import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
 import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
@@ -50,6 +51,7 @@
 /**
  * Unit tests for DynamoDBPersistenceStore using mocked DynamoDB client.
  */
+@ExtendWith(MockitoExtension.class)
 class DynamoDBPersistenceStoreTest {
     protected static final String TABLE_NAME = "idempotency_table";
     private DynamoDBPersistenceStore dynamoDBPersistenceStore;
@@ -59,7 +61,6 @@ class DynamoDBPersistenceStoreTest {
 
     @BeforeEach
     void setup() {
-        MockitoAnnotations.openMocks(this);
         dynamoDBPersistenceStore = DynamoDBPersistenceStore.builder()
                 .withTableName(TABLE_NAME)
                 .withDynamoDbClient(client)

powertools-idempotency/powertools-idempotency-dynamodb/src/test/java/software/amazon/lambda/powertools/idempotency/persistence/dynamodb/IdempotencyTest.java

@@ -22,8 +22,9 @@
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.Mock;
-import org.mockito.MockitoAnnotations;
+import org.mockito.junit.jupiter.MockitoExtension;
 
 import com.amazonaws.services.lambda.runtime.Context;
 import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent;
@@ -42,6 +43,7 @@
 import java.util.HashMap;
 import java.util.Map;
 
+@ExtendWith(MockitoExtension.class)
 class IdempotencyTest {
 
     @Mock
@@ -50,18 +52,13 @@ class IdempotencyTest {
     @Mock
     private DynamoDbClient client;
 
-    @BeforeEach
-    void setUp() {
-        MockitoAnnotations.openMocks(this);
-    }
 
     @Test
     void endToEndTest() {
         // For this test, we'll simplify and just verify that the function works with mocks
         // The important part is that our new mocking approach doesn't break existing functionality
 
         when(client.putItem(any(PutItemRequest.class))).thenReturn(null);
-        when(client.getItem(any(GetItemRequest.class))).thenReturn(GetItemResponse.builder().build());
 
         IdempotencyFunction function = new IdempotencyFunction(client);