使用 mockito.mockStatic 失败的单元测试

Question

所以，我正在编写一个 junit 测试，但我似乎无法弄清楚它失败的原因。我正在使用 Mockito.mockStatic 来模拟 InetAddres.class。一次运行所有单元测试失败。分别运行它们成功。我知道静态块被初始化一次。我似乎无法弄清楚为什么每个单元测试都没有重新初始化类 Host 。任何帮助表示赞赏

J

这是我的代码：

import org.junit.jupiter.api.Test;
import org.mockito.MockedStatic;
import org.mockito.Mockito;

import java.net.InetAddress;
import java.net.UnknownHostException;

import static org.assertj.core.api.Assertions.assertThat;


class HostTest {

    @Test
    void testLocalhost() {
        try (MockedStatic<InetAddress> inetAddressMockedStatic = Mockito.mockStatic(InetAddress.class)) {
            InetAddress inetAddress = Mockito.mock(InetAddress.class);
            Mockito.when(inetAddress.getHostName()).thenReturn("LOCALHOST");
            inetAddressMockedStatic.when(InetAddress::getLocalHost).thenReturn(inetAddress);
            assertThat(Host.getLOCALHOST()).isEqualTo("LOCALHOST");
            Mockito.reset(inetAddress);

        }
    }

    @Test
    void testIP() {
        try (MockedStatic<InetAddress> inetAddressMockedStatic = Mockito.mockStatic(InetAddress.class)) {
            InetAddress inetAddress = Mockito.mock(InetAddress.class);
            Mockito.when(inetAddress.getHostAddress()).thenReturn("127.0.0.1");
            inetAddressMockedStatic.when(InetAddress::getLocalHost).thenReturn(inetAddress);
            assertThat(Host.getIP()).isEqualTo("127.0.0.1");
        }
    }

    @Test
    void testUnkownHostExceptionIP() {
        try (MockedStatic<InetAddress> inetAddressMockedStatic = Mockito.mockStatic(InetAddress.class)) {
            inetAddressMockedStatic.when(InetAddress::getLocalHost).thenThrow(UnknownHostException.class);
            assertThat(Host.getIP()).isEqualTo("Unkown ip");
        }

    }

    @Test
    void testUnkownHostExceptionLocalhost() {
        try (MockedStatic<InetAddress> inetAddressMockedStatic = Mockito.mockStatic(InetAddress.class)) {
            inetAddressMockedStatic.when(InetAddress::getLocalHost).thenThrow(UnknownHostException.class);
            assertThat(Host.getLOCALHOST()).isEqualTo("Unkown hostname");

        }
    }
}




import java.net.InetAddress;
import java.net.UnknownHostException;

public class Host {

    private static String LOCALHOST;
    private static String IP;

    static {
        try {
            InetAddress localhost = InetAddress.getLocalHost();
            LOCALHOST = localhost.getHostName();
            IP = localhost.getHostAddress();
        } catch (UnknownHostException e) {
            LOCALHOST = "Unkown hostname";
            IP = "Unkown ip";
        }
    }

    public static String getLOCALHOST() {
        return LOCALHOST;
    }

    public static String getIP() {
        return IP;
    }
}

Answer 1

静态初始化器只执行一次，在加载类时。这意味着它只会在使用Host 类的第一个测试用例中运行。

在您的示例中，一旦testLocalhost 运行，该类将在Host.getLOCALHOST() 行中使用，此时其初始化程序已被执行。在其余的单元测试中，它永远不会再次运行。

如果你切换这些测试用例的顺序，你会得到不同的结果。

根据您的测试用例判断，您可以采取一些措施来使代码符合您的期望。由于 IP 和主机名会在您的程序执行过程中发生变化，因此它们不应该是在静态初始化程序块中设置的静态成员。

1. 摆脱共享状态。撇开并发性和内存可见性不谈，static 成员将对类的所有实例可见。省略 static 关键字并将其变为常规字段

   public class Host {
   
       private final String hostName;
   
       private final String ip;
   
       // Constructor, use this to build new instances
       public Host(String hostName, String ip) {
           this.hostName = hostName;
           this.ip = ip;
       }
   
       // No longer static, this is now an instance method
       public getHostName() {
           return this.hostName;
       }
   
       public getIp() {
           return this.ip;
       }
   }
   

2. 构建类的实例，将参数传递给构造函数以自定义其行为。

   // Host.getIp(); // If IP and host name can vary, don't make them static
   InetAddress localhost = InetAddress.getLocalHost();
   // build a new instance of Host, provide the relevant data at construction time
   Host testedHost = new Host(localhost.getHostName(), localhost.getHostAddress());
   // call the instance method, this doesn't affect your other tests
   assertThat(testedHost.getIp()).is(someIp);
   // at this point, the Host instance you created may be garbage-collected to free memory (you don't need to do that yourself)
   

   现在每个测试用例都将独立于其他测试用例。每次需要时只需创建一个 Host 的新实例。

3. 摆脱静态模拟。注意InetAddress 方法调用是如何移到Host 类之外的。通过将它们传递给构造函数，您可以使代码更易于测试。 Inversion of control 实现了。

您可以使用工厂方法来代替公共构造函数。底线是，如果您想让类改变其行为，通常最好创建新实例并封装任何状态。

静态类和成员更适合诸如在程序执行期间不会改变的不可变常量，或不依赖任何内部状态的实用方法，即pure functions。