Java程序：根据首字母判断星期几，并使用JUnit测试

下面是用Java语言编写的程序代码：

public class DayOfWeek {
    public static String getDayOfWeek(char firstLetter, char secondLetter) {
        if (firstLetter == 'M' || firstLetter == 'm') {
            return "Monday";
        } else if (firstLetter == 'T' || firstLetter == 't') {
            if (secondLetter == 'U' || secondLetter == 'u') {
                return "Tuesday";
            } else if (secondLetter == 'H' || secondLetter == 'h') {
                return "Thursday";
            }
        } else if (firstLetter == 'W' || firstLetter == 'w') {
            return "Wednesday";
        } else if (firstLetter == 'F' || firstLetter == 'f') {
            return "Friday";
        } else if (firstLetter == 'S' || firstLetter == 's') {
            if (secondLetter == 'A' || secondLetter == 'a') {
                return "Saturday";
            } else if (secondLetter == 'U' || secondLetter == 'u') {
                return "Sunday";
            }
        }
        return "Invalid input";
    }
}

下面是使用JUnit框架编写的测试类：

import org.junit.Test;
import static org.junit.Assert.assertEquals;

public class DayOfWeekTest {
    @Test
    public void testMonday() {
        assertEquals("Monday", DayOfWeek.getDayOfWeek('M', 'X'));
    }

    @Test
    public void testTuesday() {
        assertEquals("Tuesday", DayOfWeek.getDayOfWeek('T', 'U'));
    }

    @Test
    public void testThursday() {
        assertEquals("Thursday", DayOfWeek.getDayOfWeek('T', 'H'));
    }

    @Test
    public void testWednesday() {
        assertEquals("Wednesday", DayOfWeek.getDayOfWeek('W', 'X'));
    }

    @Test
    public void testFriday() {
        assertEquals("Friday", DayOfWeek.getDayOfWeek('F', 'X'));
    }

    @Test
    public void testSaturday() {
        assertEquals("Saturday", DayOfWeek.getDayOfWeek('S', 'A'));
    }

    @Test
    public void testSunday() {
        assertEquals("Sunday", DayOfWeek.getDayOfWeek('S', 'U'));
    }

    @Test
    public void testInvalidInput() {
        assertEquals("Invalid input", DayOfWeek.getDayOfWeek('X', 'X'));
    }
}

以上测试类中设计了最少的测试数据满足语句覆盖测试，每个测试方法对应一个不同的情况，使用assertEquals方法判断期望结果和实际返回值是否一致。