使用Mockito模拟某些方法，但不模拟其他方法

使用Mockito，有什么方法可以模拟类中的某些方法，而不能模拟其他方法？

例如，在这个（当然是人为设计的）Stock类中，我想模拟getPrice()和getQuantity()返回值（如下面的测试代码所示），但我想getValue()按Stock类中的编码执行乘法

public class Stock {
  private final double price;
  private final int quantity;

  Stock(double price, int quantity) {
    this.price = price;
    this.quantity = quantity;
  }

  public double getPrice() {
    return price;
  }

  public int getQuantity() {
    return quantity;
  }
  public double getValue() {
    return getPrice() * getQuantity();
  }

  @Test
  public void getValueTest() {
    Stock stock = mock(Stock.class);
    when(stock.getPrice()).thenReturn(100.00);
    when(stock.getQuantity()).thenReturn(200);
    double value = stock.getValue();
    // Unfortunately the following assert fails, because the mock Stock getValue() method does not perform the Stock.getValue() calculation code.
    assertEquals("Stock value not correct", 100.00*200, value, .00001);
}

要直接回答您的问题，是的，您可以模拟某些方法而无需模拟其他方法。这称为部分模拟。有关更多信息，请参见Mockito文档。

例如，您可以在测试中执行以下操作：

Stock stock = mock(Stock.class);
when(stock.getPrice()).thenReturn(100.00);    // Mock implementation
when(stock.getQuantity()).thenReturn(200);    // Mock implementation
when(stock.getValue()).thenCallRealMethod();  // Real implementation

在这种情况下，除非thenCallRealMethod()在when(..)子句中指定，否则将模拟每个方法的实现。

还有一种可能是使用间谍而不是模拟来代替间谍：

Stock stock = spy(Stock.class);
when(stock.getPrice()).thenReturn(100.00);    // Mock implementation
when(stock.getQuantity()).thenReturn(200);    // Mock implementation
// All other method call will use the real implementations

在那种情况下，所有方法实现都是真实的，除非您使用定义了模拟行为when(..)。

when(Object)像前面的示例一样，与间谍一起使用时，有一个重要的陷阱。真正的方法将被调用（因为在运行时stock.getPrice()先评估when(..)）。如果您的方法包含不应调用的逻辑，则可能会出现问题。您可以这样编写前面的示例：

Stock stock = spy(Stock.class);
doReturn(100.00).when(stock).getPrice();    // Mock implementation
doReturn(200).when(stock).getQuantity();    // Mock implementation
// All other method call will use the real implementations

另一种可能是使用org.mockito.Mockito.CALLS_REAL_METHODS，例如：

Stock MOCK_STOCK = Mockito.mock( Stock.class, CALLS_REAL_METHODS );

这将未打桩的调用委托给实际的实现。

但是，对于您的示例，我相信它仍然会失败，因为您所嘲笑的实现getValue()依赖于quantity和price而不是getQuantity()and getPrice()。

另一种可能性是完全避免模拟：

@Test
public void getValueTest() {
    Stock stock = new Stock(100.00, 200);
    double value = stock.getValue();
    assertEquals("Stock value not correct", 100.00*200, value, .00001);
}

通过Mito中的Spy还支持对类的部分模拟

List list = new LinkedList();
List spy = spy(list);

//optionally, you can stub out some methods:
when(spy.size()).thenReturn(100);

//using the spy calls real methods
spy.add("one");
spy.add("two");

//size() method was stubbed - 100 is printed
System.out.println(spy.size());

查看1.10.19和2.7.22文档以获取详细说明。

根据文档：

Foo mock = mock(Foo.class, CALLS_REAL_METHODS);

// this calls the real implementation of Foo.getSomething()
value = mock.getSomething();

when(mock.getSomething()).thenReturn(fakeValue);

// now fakeValue is returned
value = mock.getSomething();

您想要的是org.mockito.Mockito.CALLS_REAL_METHODS根据文档：

/**
 * Optional <code>Answer</code> to be used with {@link Mockito#mock(Class, Answer)}
 * <p>
 * {@link Answer} can be used to define the return values of unstubbed invocations.
 * <p>
 * This implementation can be helpful when working with legacy code.
 * When this implementation is used, unstubbed methods will delegate to the real implementation.
 * This is a way to create a partial mock object that calls real methods by default.
 * <p>
 * As usual you are going to read <b>the partial mock warning</b>:
 * Object oriented programming is more less tackling complexity by dividing the complexity into separate, specific, SRPy objects.
 * How does partial mock fit into this paradigm? Well, it just doesn't... 
 * Partial mock usually means that the complexity has been moved to a different method on the same object.
 * In most cases, this is not the way you want to design your application.
 * <p>
 * However, there are rare cases when partial mocks come handy: 
 * dealing with code you cannot change easily (3rd party interfaces, interim refactoring of legacy code etc.)
 * However, I wouldn't use partial mocks for new, test-driven & well-designed code.
 * <p>
 * Example:
 * <pre class="code"><code class="java">
 * Foo mock = mock(Foo.class, CALLS_REAL_METHODS);
 *
 * // this calls the real implementation of Foo.getSomething()
 * value = mock.getSomething();
 *
 * when(mock.getSomething()).thenReturn(fakeValue);
 *
 * // now fakeValue is returned
 * value = mock.getSomething();
 * </code></pre>
 */

因此，您的代码应如下所示：

import org.junit.Test;
import static org.mockito.Mockito.*;
import static org.junit.Assert.*;

public class StockTest {

    public class Stock {
        private final double price;
        private final int quantity;

        Stock(double price, int quantity) {
            this.price = price;
            this.quantity = quantity;
        }

        public double getPrice() {
            return price;
        }

        public int getQuantity() {
            return quantity;
        }

        public double getValue() {
            return getPrice() * getQuantity();
        }
    }

    @Test
    public void getValueTest() {
        Stock stock = mock(Stock.class, withSettings().defaultAnswer(CALLS_REAL_METHODS));
        when(stock.getPrice()).thenReturn(100.00);
        when(stock.getQuantity()).thenReturn(200);
        double value = stock.getValue();

        assertEquals("Stock value not correct", 100.00 * 200, value, .00001);
    }
}

要将呼叫Stock stock = mock(Stock.class);通话org.mockito.Mockito.mock(Class<T>)，看起来像这样：

 public static <T> T mock(Class<T> classToMock) {
    return mock(classToMock, withSettings().defaultAnswer(RETURNS_DEFAULTS));
}

值的文档RETURNS_DEFAULTS告诉：

/**
 * The default <code>Answer</code> of every mock <b>if</b> the mock was not stubbed.
 * Typically it just returns some empty value. 
 * <p>
 * {@link Answer} can be used to define the return values of unstubbed invocations. 
 * <p>
 * This implementation first tries the global configuration. 
 * If there is no global configuration then it uses {@link ReturnsEmptyValues} (returns zeros, empty collections, nulls, etc.)
 */

如上面的答案中所述，使用Mockito的spy方法进行部分模拟可以解决您的问题。在某种程度上，我同意，对于您的具体用例，模拟数据库查找可能更合适。根据我的经验，这并非总是可能的-至少在没有其他解决方法的情况下-我认为这非常麻烦或至少脆弱。注意，部分模拟不适用于Mockito的盟友版本。您已至少使用1.8.0。

我只会为原始问题写一个简单的注释，而不是发布此答案，但是StackOverflow不允许这样做。

再说一件事：我真的无法理解，很多问题在这里被问到“为什么要这么做”而至少没有试图理解这个问题。特别是当涉及到需要部分模拟的情况时，我确实可以想象到很多用例在什么地方有用。这就是Mockito的家伙提供该功能的原因。当然，不应过度使用此功能。但是，当我们谈论无法通过非常复杂的方式建立的测试用例设置时，应该使用间谍程序。