java - JMockit 模拟 System.currentTimeMillis()

Question

运行这个测试:

@Test
public void testSystemCurrentTimeMillis() {
    new NonStrictExpectations(System.class) {{
        System.currentTimeMillis(); result = 1438357206679L;
    }};
    long currentTime = System.currentTimeMillis();
    assertEquals(1438357206679L, currentTime);
}

我得到一个 IllegalStateException:

java.lang.IllegalStateException: Missing invocation to mocked type at this point; please make sure such invocations appear only after the declaration of a suitable mock field or parameter
    at unittests.DateTest$1.(DateTest.java:24)
    at unittests.DateTest.testSystemCurrentTimeMillis(DateTest.java:23)

我的测试 (JMockit 1.18) 有什么问题？

Answer 1

我的最终解决方案是为 System 创建一个 MockUp，它只模拟 currentTimeMillis() 方法:

private static class SystemMock extends MockUp<System> {
    @Mock
    public static long currentTimeMillis() {
        return 10000000L;
    }
}

@Test
public void testAddNowDate() {
    new SystemMock();
    long currentTime = System.currentTimeMillis();
    assertEquals(10000000L, currentTime);
}