如何为NextDay类设计一个JUnit测试，实现100%判定覆盖？并请提供NextDay类的相关代码供测试用例参考。

NextDay类是一个假设的日历类，它有一个方法`calculateDaysUntilNextInstanceOf()`，该方法接收一个日期作为输入，并返回到下一个特定类型的日期（例如星期一、星期五等）所需的天数。为了实现100%的判定覆盖，我们需要编写测试用例，确保所有可能的输入情况都被包括进去。

首先，我们假设NextDay类的代码如下：

import java.time.LocalDate;

public class NextDay {
    public int calculateDaysUntilNextInstanceOf(LocalDate date, DayOfWeek targetDay) {
        return (int) Math.ceil(date.until(getNextDate(date, targetDay), ChronoUnit.DAYS));
    }

    private LocalDate getNextDate(LocalDate date, DayOfWeek targetDay) {
        // 这里假设有一些复杂的日历处理逻辑
        return date.plusWeeks(1).with(targetDay);
    }
}

接下来，我们可以创建一个JUnit测试类，包含一些测试用例来覆盖各种场景：

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;
import java.time.DayOfWeek;
import java.time.LocalDate;

class NextDayTest {

    @Test
    void testCalculateDaysUntilNextInstanceOfMonday() {
        // 测试今天是周一的情况
        LocalDate today = LocalDate.now().with(DayOfWeek.MONDAY);
        assertEquals(0, new NextDay().calculateDaysUntilNextInstanceOf(today, DayOfWeek.MONDAY));

        // 测试今天不是周一，但是一周内有周一的情况
        today = LocalDate.now().with(DayOfWeek.TUESDAY);
        assertEquals(7, new NextDay().calculateDaysUntilNextInstanceOf(today, DayOfWeek.MONDAY));
    }

    @Test
    void testCalculateDaysUntilNextInstanceOfFriday() {
        // 类似地，测试周五的情况
        LocalDate today = LocalDate.now().with(DayOfWeek.FRIDAY);
        assertEquals(0, new NextDay().calculateDaysUntilNextInstanceOf(today, DayOfWeek.FRIDAY));
        today = LocalDate.now().with(DayOfWeek.SATURDAY);
        assertEquals(4, new NextDay().calculateDaysUntilNextInstanceOf(today, DayOfWeek.FRIDAY));
    }

    // 添加更多测试用例，确保其他边界条件和异常情况也被覆盖
    @Test
    void testInvalidDayOfWeek() {
        LocalDate invalidDate = LocalDate.now();
        assertThrows(IllegalArgumentException.class, () -> new NextDay().calculateDaysUntilNextInstanceOf(invalidDate, DayOfWeek.WEEKEND));
    }

    // 其他测试用例...
}