如何模拟实现类？

Question

我有这样的事情：

public interface SomeInterface {
    public String someMethod(String someArg1, String someArg2);
}

public class SomeInterfaceImpl {

    @Override
    public String someMethod(String someArg1, String someArg2) {
        String response;

        // a REST API call which fetches response (need to mock this)

        return response;
    }
}

public class SomeClass {

    public int execute() {

        int returnValue;

        // some code

        SomeInterface someInterface = new SomeInterfaceImpl();
        String response = someInterface.someMethod("some1", "some2");

        // some code

        return returnValue;
    }
}

我想使用 JUnit 测试 SomeClass 中的 execute() 方法。由于someMethod(String someArg1, String someArg2) 调用了一个REST API，我想模拟someMethod 以返回一些预定义的响应。但不知何故，真正的someMethod 被调用而不是返回预定义的响应。如何让它发挥作用？

这是我尝试使用 Mockito 和 PowerMockito 的方法：

@RunWith(PowerMockRunner.class)
@PrepareForTest({ SomeInterface.class, SomeInterfaceImpl.class, SomeClass.class })
public class SomeClassTest {

    @Test
    public void testExecute() {
        String predefinedResponse = "Some predefined response";
        int expectedReturnValue = 10;

        SomeInterfaceImpl impl = PowerMockito.mock(SomeInterfaceImpl.class);
        PowerMockito.whenNew(SomeInterfaceImpl.class).withAnyArguments().thenReturn(impl);
        PowerMockito.when(impl.someMethod(Mockito.any(), Mockito.any())).thenReturn(predefinedResponse);

        SomeClass someClass = new SomeClass();
        int actualReturnValue = someClass.execute();
        assertEquals(expectedReturnValue, actualReturnValue);
      }
}

Answer 1

您不必这样做。

您将被测方法更改为不直接调用 new。

例如，您使用依赖注入。

是的，这可以通过 Powermock 完成，但请相信我：这样做是错误的方法！

Answer 2

这里是一个没有框架的注入依赖的例子：

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;

import static org.junit.Assert.assertEquals;
import static org.mockito.Matchers.anyString;
import static org.mockito.Mockito.when;

interface SomeInterface {
  String someMethod(String someArg1, String someArg2);
}

class SomeInterfaceImpl implements SomeInterface {

  @Override
  public String someMethod(String someArg1, String someArg2) {
    String response;

    response = "the answer.";// a REST API call which fetches response (need to mock this)

    return response;
  }
}

class SomeClass {
  private final SomeInterface someInterface;

  SomeClass(final SomeInterface someInterface) {
    this.someInterface = someInterface;
  }

  public SomeClass() {
    this(new SomeInterfaceImpl());
  }

  public int execute() {

    int returnValue;

    // some code

    String response = someInterface.someMethod("some1", "some2");

    returnValue = 42; // some code

    return returnValue;
  }
}

@RunWith(MockitoJUnitRunner.class)
class SomeClassTest {
  private static final String SOME_PREDEFINED_RESPONSE = "Some predefined response";
  @Mock
  private SomeInterface someInterface;
  @InjectMocks
  private SomeClass underTest;

  @Before
  public void setup() {
    when(someInterface.someMethod(anyString(), anyString())).thenReturn(SOME_PREDEFINED_RESPONSE);
  }

  @Test
  public void testExecute() {
    int expectedReturnValue = 42;
    int actualReturnValue = underTest.execute();
    assertEquals(expectedReturnValue, actualReturnValue);
  }
}

Answer 3

这个答案与 Andreas 发布的答案非常相似，唯一的区别是您可以使用 @RunWith(SpringRunner.class) 运行它，它将避免 bean 实例化和额外配置的问题。避免使用 Powermocks，仅在需要模拟静态类时使用它。

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;

import org.springframework.test.context.junit4.SpringRunner;

import static org.junit.Assert.assertEquals;
import static org.mockito.Matchers.anyString;
import static org.mockito.Mockito.when;

interface SomeInterface {
  String someMethod(String someArg1, String someArg2);
}

class SomeInterfaceImpl implements SomeInterface {

  @Override
  public String someMethod(String someArg1, String someArg2) {
    String response;

    response = "the answer.";// a REST API call which fetches response (need to mock this)

    return response;
  }
}

class SomeClass {
  private final SomeInterface someInterface;

  SomeClass(final SomeInterface someInterface) {
    this.someInterface = someInterface;
  }

  public SomeClass() {
    this(new SomeInterfaceImpl());
  }

  public int execute() {

    int returnValue;

    // some code

    String response = someInterface.someMethod("some1", "some2");

    returnValue = 42; // some code

    return returnValue;
  }
}

@RunWith(MockitoJUnitRunner.class)
class SomeClassTest {
  private static final String SOME_PREDEFINED_RESPONSE = "Some predefined response";
  @Mock
  private SomeInterface someInterface;
  @InjectMocks
  private SomeClass underTest;

  @Before
  public void setup() {
    when(someInterface.someMethod(anyString(), anyString())).thenReturn(SOME_PREDEFINED_RESPONSE);
  }

  @Test
  public void testExecute() {
    int expectedReturnValue = 42;
    int actualReturnValue = underTest.execute();
    assertEquals(expectedReturnValue, actualReturnValue);
  }
}