feat: Add test coverage for single-table-inheritance pattern (#3468)

* Add STI tests

* test: add delta for floating-point comparison in VehicleServiceTest

* fix: guard teardown against nulls and use assertNotNull in VehicleServiceTest

Add null checks in @AfterEach tearDown() to prevent NullPointerException
if setUp() partially fails. Replace assertTrue(x != null) with assertNotNull(x).

* style: format code in SingleTableInheritanceTest and VehicleServiceTest for consistency

single-table-inheritance/src/test/java/com/iluwatar/SingleTableInheritanceTest.java

@@ -0,0 +1,38 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.api.Test;
+
+/** Tests that SingleTableInheritance example application runs without errors. */
+class SingleTableInheritanceTest {
+
+  @Test
+  void shouldExecuteWithoutException() {
+    assertDoesNotThrow(() -> SingleTableInheritance.main(new String[] {}));
+  }
+}

single-table-inheritance/src/test/java/com/iluwatar/service/VehicleServiceTest.java

@@ -0,0 +1,161 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.service;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.iluwatar.entity.Car;
+import com.iluwatar.entity.Freighter;
+import com.iluwatar.entity.Train;
+import com.iluwatar.entity.Truck;
+import com.iluwatar.entity.Vehicle;
+import java.util.List;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+
+/**
+ * Tests for {@link VehicleService} exercising CRUD operations and verifying that all concrete
+ * Vehicle subtypes are persisted and retrieved correctly via the single-table inheritance strategy.
+ */
+@SpringBootTest
+class VehicleServiceTest {
+
+  private static final double DELTA = 0.001;
+
+  @Autowired private VehicleService vehicleService;
+
+  private Vehicle savedCar;
+  private Vehicle savedTruck;
+  private Vehicle savedTrain;
+  private Vehicle savedFreighter;
+
+  @BeforeEach
+  void setUp() {
+    savedCar = vehicleService.saveVehicle(new Car("Tesla", "Model S", 4, 825));
+    savedTruck = vehicleService.saveVehicle(new Truck("Ford", "F-150", 3325, 14000));
+    savedTrain = vehicleService.saveVehicle(new Train("Siemens", "Velaro", 600, 8));
+    savedFreighter = vehicleService.saveVehicle(new Freighter("Boeing", "747F", 100000, 8130));
+  }
+
+  @AfterEach
+  void tearDown() {
+    if (savedCar != null) vehicleService.deleteVehicle(savedCar);
+    if (savedTruck != null) vehicleService.deleteVehicle(savedTruck);
+    if (savedTrain != null) vehicleService.deleteVehicle(savedTrain);
+    if (savedFreighter != null) vehicleService.deleteVehicle(savedFreighter);
+  }
+
+  @Test
+  void saveVehicle_shouldPersistCarWithCorrectType() {
+    assertTrue(savedCar.getVehicleId() > 0);
+    assertInstanceOf(Car.class, savedCar);
+    assertEquals("Tesla", savedCar.getManufacturer());
+    assertEquals("Model S", savedCar.getModel());
+    assertEquals(825, ((Car) savedCar).getEngineCapacity());
+  }
+
+  @Test
+  void saveVehicle_shouldPersistTruckWithCorrectType() {
+    assertTrue(savedTruck.getVehicleId() > 0);
+    assertInstanceOf(Truck.class, savedTruck);
+    assertEquals(14000, ((Truck) savedTruck).getTowingCapacity());
+  }
+
+  @Test
+  void saveVehicle_shouldPersistTrainWithCorrectType() {
+    assertTrue(savedTrain.getVehicleId() > 0);
+    assertInstanceOf(Train.class, savedTrain);
+    assertEquals(8, ((Train) savedTrain).getNoOfCarriages());
+  }
+
+  @Test
+  void saveVehicle_shouldPersistFreighterWithCorrectType() {
+    assertTrue(savedFreighter.getVehicleId() > 0);
+    assertInstanceOf(Freighter.class, savedFreighter);
+    assertEquals(8130.0, ((Freighter) savedFreighter).getFlightLength(), DELTA);
+  }
+
+  @Test
+  void getVehicle_shouldReturnCorrectVehicleById() {
+    Vehicle fetched = vehicleService.getVehicle(savedCar.getVehicleId());
+
+    assertNotNull(fetched);
+    assertInstanceOf(Car.class, fetched);
+    assertEquals(savedCar.getVehicleId(), fetched.getVehicleId());
+  }
+
+  @Test
+  void getVehicle_shouldReturnNullForNonexistentId() {
+    Vehicle result = vehicleService.getVehicle(Integer.MAX_VALUE);
+    assertNull(result);
+  }
+
+  @Test
+  void getAllVehicles_shouldReturnAllSavedVehicles() {
+    List<Vehicle> all = vehicleService.getAllVehicles();
+    assertNotNull(all);
+    // At minimum the 4 vehicles saved in @BeforeEach must be present
+    assertTrue_containsId(all, savedCar.getVehicleId());
+    assertTrue_containsId(all, savedTruck.getVehicleId());
+    assertTrue_containsId(all, savedTrain.getVehicleId());
+    assertTrue_containsId(all, savedFreighter.getVehicleId());
+  }
+
+  @Test
+  void updateVehicle_shouldPersistChanges() {
+    Car car = (Car) savedCar;
+    car.setModel("Model X");
+    vehicleService.updateVehicle(car);
+
+    Vehicle updated = vehicleService.getVehicle(car.getVehicleId());
+    assertEquals("Model X", updated.getModel());
+  }
+
+  @Test
+  void deleteVehicle_shouldRemoveFromRepository() {
+    // Save a temporary vehicle and delete it
+    Vehicle tmp = vehicleService.saveVehicle(new Car("BMW", "M3", 4, 3000));
+    int tmpId = tmp.getVehicleId();
+
+    vehicleService.deleteVehicle(tmp);
+
+    assertNull(vehicleService.getVehicle(tmpId));
+  }
+
+  // Helper: assert that a specific vehicle id exists in the list
+  private void assertTrue_containsId(List<Vehicle> vehicles, int id) {
+    boolean found = vehicles.stream().anyMatch(v -> v.getVehicleId() == id);
+    if (!found) {
+      throw new AssertionError("Expected vehicle with id=" + id + " in list but was not found.");
+    }
+  }
+}