如何使用JMockit模拟Calendar.getInstance方法？

Question

我试图使用JMockit模拟Calendar.getInstance()方法。 这是我第一次嘲笑任何东西。

下面是我的方法，它以YYYYMMDD的格式给出了最近一个Monday或最近Thursday的日期。

今天是星期天，因此它应该以YYYYMMDD的格式返回星期四的日期，所以它将是 - 2014027

public static String getCorrectDate() {

    Calendar cal = Calendar.getInstance();

    try {
        int dow = cal.get(Calendar.DAY_OF_WEEK);
        switch (dow) {
        case Calendar.THURSDAY:
        case Calendar.FRIDAY:
        case Calendar.SATURDAY:
        case Calendar.SUNDAY:
        while (cal.get(Calendar.DAY_OF_WEEK) != Calendar.THURSDAY) {
            cal.add(Calendar.DATE, -1);
        }
        break;
        case Calendar.MONDAY:
        case Calendar.TUESDAY:
        case Calendar.WEDNESDAY:
        while (cal.get(Calendar.DAY_OF_WEEK) != Calendar.MONDAY) {
            cal.add(Calendar.DATE, -1);
        }
        break;
        }
    } catch (Exception ex) {
        // log error
    }

    return toDateFormat.format(cal.getTime());
}

所以我的问题是我如何使用JMokcit模拟Calendar.getInstance方法，这样我可以轻松地使用junit getCorrectDate方法？

我以前从未嘲笑它，所以我面临一些问题？

任何人都可以在我的例子中提供一个简单的例子吗？

我试图这样做，但它在MockClass抱怨我，因为它无法解决..我已经添加了JMockit的maven依赖

@MockClass(realClass = Calendar.class) 
class CalendarMock {
 private int hour;
 private int day;
 private int minute;

 public CalendarMock(int day, int hour, int minute) {
  this.hour = hour;
  this.day = day;
  this.minute = minute;
 }

 @Mock
 public int get(int id) {
  if (id == Calendar.HOUR_OF_DAY) {
   return hour;
  }
  if (id == Calendar.DAY_OF_WEEK) {
   return day;
  }

  if (id == Calendar.MINUTE) {
   return minute;
  }
  return -1;
 }
}

Answer 1

public class CalendarTest {

    @Test
    public void testCalender() {

        new MockCalendar(1,2,3);

        Calendar c = Calendar.getInstance();
        int day = c.get(Calendar.HOUR_OF_DAY);
        Assert.assertEquals(day, 2);
    }

  public static class MockCalendar extends MockUp<Calendar> {
        private int hour;
        private int minute;
        private int day;

        public MockCalendar(int day, int hour, int minute) {
            this.hour = hour;
            this.minute = minute;
            this.day = day;
        }
        @Mock
        protected void $init() {}

        @Mock
        public static Calendar getInstance() {
            return new GregorianCalendar(1970,1,1);
        }

        @Mock
        public int get(int id) {
            if (id == Calendar.HOUR_OF_DAY) {
                return hour;
            }
            if (id == Calendar.DAY_OF_WEEK) {
                return day;
            }

            if (id == Calendar.MINUTE) {
                return minute;
            }
            return -1;
        }
    }
 }

}

你可以增强get逻辑来做东西。

Answer 2

我强烈建议在这些方面引入一个Clock接口，而不是试图在这里模拟一个静态方法：

public interface Clock {
    Date now(); // Or long, or Instant if you're using Joda Time
}

然后，您可以拥有一个使用new Date()或System.currentTimeMillis的生产实现，以及一个可以设置“当前时间”的测试实现。 将时钟传递给方法，或使其成为实例方法，并使用适当的时钟“配置”实例（例如，在构造函数中）。

Clock接口使您的代码更容易根据我的经验进行测试，而不必依赖相对高级的模拟功能来模拟静态方法。

所以你的生产代码会变成：

public static String getCorrectDate(Clock clock) {
    Calendar cal = new GregorianCalendar();
    cal.setTimeZone(...); // Which time zone are you interested in?
    cal.setTime(clock.now()); // Or cal.setTimeInMillis(clock.now());

    // ... logic as before
}

现在，您可以使用许多不同的日期和时间对其进行测试。

Answer 3

这是getCorrectDate()方法的完整测试类（减去导入），使用JMockit 1.6中提供的两个getCorrectDate() API：

public class DateAdjustmentTest
{
    final int year = 2014;
    final int month = Calendar.MARCH;
    final Calendar[] datesOnDifferentWeekdays = {
        new GregorianCalendar(year, month, 2), // a sunday
        new GregorianCalendar(year, month, 3), // a monday
        new GregorianCalendar(year, month, 4), // a tuesday
        new GregorianCalendar(year, month, 5), // a wednesday
        new GregorianCalendar(year, month, 6), // a thursday
        new GregorianCalendar(year, month, 7), // a friday
        new GregorianCalendar(year, month, 8), // a saturday
    };

    @Test
    public void getAdjustedDateAccordingToWeekday_usingExpectationsAPI()
    {
        new NonStrictExpectations(Calendar.class) {{
            // Each consecutive call to this method will return the next date.
            // Calls to other Calendar methods will not be mocked.
            Calendar.getInstance(); result = datesOnDifferentWeekdays;
        }};

        assertEachDayOfWeekGetsCorrectlyAdjusted();
    }

    void assertEachDayOfWeekGetsCorrectlyAdjusted()
    {
        String thursdayOfPreviousWeek = "27/02/2014";
        assertEquals(thursdayOfPreviousWeek, getCorrectDate());

        String mondayOfSameWeek = "03/03/2014";
        assertEquals(mondayOfSameWeek, getCorrectDate());
        assertEquals(mondayOfSameWeek, getCorrectDate());
        assertEquals(mondayOfSameWeek, getCorrectDate());

        String thursdayOfSameWeek = "06/03/2014";
        assertEquals(thursdayOfSameWeek, getCorrectDate());
        assertEquals(thursdayOfSameWeek, getCorrectDate());
        assertEquals(thursdayOfSameWeek, getCorrectDate());
    }

    @Test
    public void getAdjustedDateAccordingToWeekday_usingMockUpAPI()
    {
        new MockUp<Calendar>() {
            @Mock
            Calendar getInstance(Invocation inv)
            {
                return datesOnDifferentWeekdays[inv.getInvocationIndex()];
            }
        };

        assertEachDayOfWeekGetsCorrectlyAdjusted();
    }
}

我想说两个测试都非常简单，无需更改原始生产代码。