unit-testing - 为什么我必须扩展 PowerMockTestCase？

Question

下面的测试抛出 java.lang.IllegalStateException: no last call on a mock available当我不从 PowerMockTestCase 扩展时。

一旦我从 PowerMockTestCase 扩展，错误就会消失。为什么会发生这种情况？

import static org.junit.Assert.assertEquals;

import org.easymock.EasyMock;
import org.powermock.api.easymock.PowerMock;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.testng.PowerMockTestCase;

@PrepareForTest({ IdGenerator.class, ServiceRegistartor.class })
public class SnippetTest extends PowerMockTestCase{

    @org.testng.annotations.Test
    public void testRegisterService() throws Exception {
        long expectedId = 42;

        // We create a new instance of test class under test as usually.
        ServiceRegistartor tested = new ServiceRegistartor();

        // This is the way to tell PowerMock to mock all static methods of a
        // given class
        PowerMock.mockStatic(IdGenerator.class);

        /*
         * The static method call to IdGenerator.generateNewId() expectation.
         * This is why we need PowerMock.
         */
        EasyMock.expect(IdGenerator.generateNewId()).andReturn(expectedId).once();

        // Note how we replay the class, not the instance!
        PowerMock.replay(IdGenerator.class);

        long actualId = tested.registerService(new Object());

        // Note how we verify the class, not the instance!
        PowerMock.verify(IdGenerator.class);

        // Assert that the ID is correct
        assertEquals(expectedId, actualId);
    }

}

Answer 1

在使用 PowerMock 进行静态模拟时，会发生一个类级别的工具来使您的模拟工作。 PowerMockTestCase 类有一个代码(方法 beforePowerMockTestClass())将您的常规类加载器切换到协调模拟注入(inject)的 powermock 类加载器。因此，您需要扩展此类以使静态模拟起作用。