Java JUnit单元测试：验证方法返回的对象、空值及特定实例

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

// 假设存在以下类结构
class Feedback {
    private String message;
    private int rating;

    public Feedback(String message, int rating) {
        this.message = message;
        this.rating = rating;
    }

    // 省略 getter/setter，以及 equals/hashCode 方法（稍后会讨论）
}

class ItemClass {
    public Feedback getFeedback(String itemId) {
        if ("invalidId".equals(itemId)) {
            return null; // 无效ID返回null
        }
        if ("item123".equals(itemId)) {
            return new Feedback("Good product!", 5);
        }
        return new Feedback("Default feedback", 3);
    }
}

public class ItemClassTest {

    @Test
    void testGetFeedbackReturnsNullForInvalidId() {
        ItemClass itemClass = new ItemClass();
        Feedback feedback = itemClass.getFeedback("invalidId");
        assertNull(feedback, "当ID无效时，getFeedback方法应返回null");
    }
}

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class ItemClassTest {

    // ... (ItemClass 和 Feedback 定义同上) ...

    @Test
    void testGetFeedbackReturnsCorrectType() {
        ItemClass itemClass = new ItemClass();
        Feedback feedback = itemClass.getFeedback("item123");
        assertNotNull(feedback, "反馈对象不应为null"); // 先确保不是null
        assertTrue(feedback instanceof Feedback, "返回的对象应是Feedback类型");
    }
}

import java.util.Objects;

class Feedback {
    private String message;
    private int rating;

    public Feedback(String message, int rating) {
        this.message = message;
        this.rating = rating;
    }

    public String getMessage() { return message; }
    public int getRating() { return rating; }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Feedback feedback = (Feedback) o;
        return rating == feedback.rating &&
               Objects.equals(message, feedback.message);
    }

    @Override
    public int hashCode() {
        return Objects.hash(message, rating);
    }

    @Override
    public String toString() { // 有助于调试
        return "Feedback{message='" + message + "', rating=" + rating + '}';
    }
}

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class ItemClassTest {

    // ... (ItemClass 和重写 equals/hashCode 的 Feedback 定义同上) ...

    @Test
    void testGetFeedbackReturnsSpecificFeedback() {
        ItemClass itemClass = new ItemClass();
        // 预期返回的Feedback对象
        Feedback expectedFeedback = new Feedback("Good product!", 5);

        // 实际从方法中获取的Feedback对象
        Feedback actualFeedback = itemClass.getFeedback("item123");

        assertNotNull(actualFeedback, "实际反馈对象不应为null");
        assertEquals(expectedFeedback, actualFeedback, "返回的Feedback对象应与预期值相等");
    }
}

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

// 假设 ItemClass 有一个方法总是返回同一个 Feedback 实例 (例如，一个缓存的默认反馈)
class ItemClassWithCachedFeedback {
    private static final Feedback DEFAULT_FEEDBACK = new Feedback("Default feedback", 3);

    public Feedback getDefaultFeedback() {
        return DEFAULT_FEEDBACK; // 总是返回同一个实例
    }
}

public class ItemClassTest {

    // ... (Feedback 定义同上) ...

    @Test
    void testGetDefaultFeedbackReturnsSameInstance() {
        ItemClassWithCachedFeedback itemClass = new ItemClassWithCachedFeedback();
        Feedback feedback1 = itemClass.getDefaultFeedback();
        Feedback feedback2 = itemClass.getDefaultFeedback();

        // 验证两次调用是否返回了同一个对象引用
        assertSame(feedback1, feedback2, "两次调用getDefaultFeedback应返回同一个对象实例");
    }
}

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class ItemClassComprehensiveTest {

    private ItemClass itemClass;

    @BeforeEach // 在每个测试方法执行前初始化
    void setUp() {
        itemClass = new ItemClass();
    }

    @Test
    void testGetFeedbackForValidItem() {
        Feedback expected = new Feedback("Good product!", 5);
        Feedback actual = itemClass.getFeedback("item123");

        assertNotNull(actual, "返回的反馈不应为null");
        assertEquals(expected, actual, "返回的反馈内容应符合预期");
        assertTrue(actual instanceof Feedback, "返回对象应为Feedback类型");
    }

    @Test
    void testGetFeedbackForInvalidItem() {
        Feedback actual = itemClass.getFeedback("invalidId");
        assertNull(actual, "无效ID应返回null");
    }

    @Test
    void testGetFeedbackForUnknownItem() {
        Feedback expectedDefault = new Feedback("Default feedback", 3);
        Feedback actual = itemClass.getFeedback("unknownId");

        assertNotNull(actual, "未知ID也应返回非null反馈");
        assertEquals(expectedDefault, actual, "未知ID应返回默认反馈");
    }
}