eugenp · jzheaux · Mar 22, 2025 · Mar 9, 2025 · Mar 9, 2025 · Mar 10, 2025
diff --git a/persistence-modules/core-java-persistence-4/pom.xml b/persistence-modules/core-java-persistence-4/pom.xml
@@ -47,6 +47,13 @@
             <artifactId>spring-boot-starter</artifactId>
             <version>${springframework.boot.spring-boot-starter.version}</version>
         </dependency>
+
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-junit-jupiter</artifactId>
+            <version>5.16.0</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>

diff --git a/...nce-modules/core-java-persistence-4/src/main/java/com/baeldung/jdbc/mocking/Customer.java b/...nce-modules/core-java-persistence-4/src/main/java/com/baeldung/jdbc/mocking/Customer.java
@@ -0,0 +1,8 @@
+package com.baeldung.jdbc.mocking;
+
+public record Customer(int id, String name, Status status) {
+
+    public enum Status {
+        ACTIVE, LOYAL, INACTIVE
+    }
+}
diff --git a/...les/core-java-persistence-4/src/main/java/com/baeldung/jdbc/mocking/CustomersService.java b/...les/core-java-persistence-4/src/main/java/com/baeldung/jdbc/mocking/CustomersService.java
@@ -0,0 +1,45 @@
+package com.baeldung.jdbc.mocking;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.sql.DataSource;
+
+import com.baeldung.jdbc.mocking.Customer.Status;
+
+public class CustomersService {
+
+    private final DataSource dataSource;
+
+    public CustomersService(DataSource dataSource) {
+        this.dataSource = dataSource;
+    }
+
+    public List<Customer> customersEligibleForOffers() throws SQLException {
+        try (Connection conn = dataSource.getConnection(); Statement stmt = conn.createStatement()) {
+            ResultSet resultSet = stmt.executeQuery("SELECT * FROM customers");
+            List<Customer> customers = new ArrayList<>();
+
+            while (resultSet.next()) {
+                Customer customer = mapCustomer(resultSet);
+                if (customer.status() == Status.ACTIVE || customer.status() == Status.LOYAL) {
+                    customers.add(customer);
+                }
+            }
+            return customers;
+        }
+    }
+
+    private Customer mapCustomer(ResultSet resultSet) throws SQLException {
+        return new Customer(
+            resultSet.getInt("id"),
+            resultSet.getString("name"),
+            Status.valueOf(resultSet.getString("status"))
+        );
+    }
+
+}
diff --git a/...ules/core-java-persistence-4/src/main/java/com/baeldung/jdbc/mocking/v2/AllCustomers.java b/...ules/core-java-persistence-4/src/main/java/com/baeldung/jdbc/mocking/v2/AllCustomers.java
@@ -0,0 +1,41 @@
+package com.baeldung.jdbc.mocking.v2;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Supplier;
+
+import javax.sql.DataSource;
+
+import com.baeldung.jdbc.mocking.Customer;
+
+public class AllCustomers implements Supplier<List<Customer>> {
+
+    private final DataSource dataSource;
+
+    @Override
+    public List<Customer> get() {
+        try (Connection conn = dataSource.getConnection(); Statement stmt = conn.createStatement()) {
+            ResultSet resultSet = stmt.executeQuery("SELECT * FROM customers");
+            List<Customer> customers = new ArrayList<>();
+            while (resultSet.next()) {
+                customers.add(mapCustomer(resultSet));
+            }
+            return customers;
+        } catch (SQLException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public AllCustomers(DataSource dataSource) {
+        this.dataSource = dataSource;
+    }
+
+    private Customer mapCustomer(ResultSet resultSet) throws SQLException {
+        return new Customer(resultSet.getInt("id"), resultSet.getString("name"), Customer.Status.valueOf(resultSet.getString("status")));
+    }
+
+}
diff --git a/...ore-java-persistence-4/src/main/java/com/baeldung/jdbc/mocking/v2/CustomersServiceV2.java b/...ore-java-persistence-4/src/main/java/com/baeldung/jdbc/mocking/v2/CustomersServiceV2.java
@@ -0,0 +1,24 @@
+package com.baeldung.jdbc.mocking.v2;
+
+import java.util.List;
+import java.util.function.Supplier;
+
+import com.baeldung.jdbc.mocking.Customer;
+import com.baeldung.jdbc.mocking.Customer.Status;
+
+public class CustomersServiceV2 {
+
+    private final Supplier<List<Customer>> findAllCustomers;
+
+    public List<Customer> customersEligibleForOffers() {
+        return findAllCustomers.get()
+          .stream()
+          .filter(customer -> customer.status() == Status.ACTIVE || customer.status() == Status.LOYAL)
+          .toList();
+    }
+
+    public CustomersServiceV2(Supplier<List<Customer>> findAllCustomers) {
+        this.findAllCustomers = findAllCustomers;
+    }
+
+}
diff --git a/...ava-persistence-4/src/test/java/com/baeldung/jdbc/mocking/JdbcMockingIntegrationTest.java b/...ava-persistence-4/src/test/java/com/baeldung/jdbc/mocking/JdbcMockingIntegrationTest.java
@@ -0,0 +1,36 @@
+package com.baeldung.jdbc.mocking;
+
+import static org.assertj.core.api.AssertionsForInterfaceTypes.assertThat;
+
+import java.sql.SQLException;
+import java.util.List;
+
+import org.h2.jdbcx.JdbcDataSource;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import com.baeldung.jdbc.mocking.Customer.Status;
+
+class JdbcMockingIntegrationTest {
+
+    private static JdbcDataSource dataSource;
+
+    @BeforeAll
+    static void setUp() {
+        dataSource = new JdbcDataSource();
+        dataSource.setURL("jdbc:h2:mem:testdb;DB_CLOSE_DELAY=-1;INIT=RUNSCRIPT FROM 'classpath:data.sql'");
+        dataSource.setUser("sa");
+        dataSource.setPassword("");
+    }
+
+    @Test
+    void whenFetchingCustomersEligibleForOffers_thenTheyHaveActiveOrLoyalStatus() throws SQLException {
+        CustomersService customersService = new CustomersService(dataSource);
+
+        List<Customer> customers = customersService.customersEligibleForOffers();
+
+        assertThat(customers).extracting(Customer::status)
+            .containsOnly(Status.ACTIVE, Status.LOYAL);
+    }
+
+}
diff --git a/.../core-java-persistence-4/src/test/java/com/baeldung/jdbc/mocking/JdbcMockingUnitTest.java b/.../core-java-persistence-4/src/test/java/com/baeldung/jdbc/mocking/JdbcMockingUnitTest.java
@@ -0,0 +1,76 @@
+package com.baeldung.jdbc.mocking;
+
+import static org.assertj.core.api.AssertionsForInterfaceTypes.assertThat;
+import static org.mockito.Mockito.when;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.Statement;
+import java.util.List;
+
+import javax.sql.DataSource;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import com.baeldung.jdbc.mocking.Customer.Status;
+import com.baeldung.jdbc.mocking.v2.CustomersServiceV2;
+
+@ExtendWith(MockitoExtension.class)
+class JdbcMockingUnitTest {
+
+    @Mock
+    DataSource dataSource;
+    @Mock
+    Connection conn;
+    @Mock
+    Statement stmt;
+    @Mock
+    ResultSet resultSet;
+
+    @Test
+    void whenFetchingEligibleCustomers_thenTheyHaveCorrectStatus() throws Exception {
+        //given
+        CustomersService customersService = new CustomersService(dataSource);
+
+        when(dataSource.getConnection())
+          .thenReturn(conn);
+        when(conn.createStatement())
+          .thenReturn(stmt);
+        when(stmt.executeQuery("SELECT * FROM customers"))
+           .thenReturn(resultSet);
+
+        when(resultSet.next())
+          .thenReturn(true, true, true, false);
+        when(resultSet.getInt("id"))
+          .thenReturn(1, 2, 3);
+        when(resultSet.getString("name"))
+          .thenReturn("Alice", "Bob", "John");
+        when(resultSet.getString("status"))
+          .thenReturn("LOYAL", "ACTIVE", "INACTIVE");
+
+        // when
+        List<Customer> eligibleCustomers = customersService.customersEligibleForOffers();
+
+        // then
+        assertThat(eligibleCustomers).containsExactlyInAnyOrder(new Customer(1, "Alice", Status.LOYAL), new Customer(2, "Bob", Status.ACTIVE));
+    }
+
+    @Test
+    void whenFetchingEligibleCustomersFromV2_thenTheyHaveCorrectStatus() {
+        // given
+        List<Customer> allCustomers = List.of(new Customer(1, "Alice", Status.LOYAL), new Customer(2, "Bob", Status.ACTIVE),
+            new Customer(3, "John", Status.INACTIVE));
+
+        CustomersServiceV2 service = new CustomersServiceV2(() -> allCustomers);
+
+        // when
+        List<Customer> eligibleCustomers = service.customersEligibleForOffers();
+
+        // then
+        assertThat(eligibleCustomers).containsExactlyInAnyOrder(new Customer(1, "Alice", Status.LOYAL), new Customer(2, "Bob", Status.ACTIVE));
+    }
+
+}
diff --git a/persistence-modules/core-java-persistence-4/src/test/resources/data.sql b/persistence-modules/core-java-persistence-4/src/test/resources/data.sql
@@ -0,0 +1,4 @@
+create table customers (id int primary key, name varchar(255), status varchar(255));
+insert into customers (id, name, status) values (1, 'Alice', 'LOYAL');
+insert into customers (id, name, status) values (2, 'Bob', 'ACTIVE');
+insert into customers (id, name, status) values (3, 'Charlie', 'INACTIVE');