一、下面是两个单元测试的实例：

第一个是计算时间的，展示的时间距离现在过了多久。可以找一个固定时间，看时间比较返回的结果与预期是否相似。

- (void)test59SecondsAgo{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2019-12-14 10:59:01"];
    NSAssert([timeString isEqualToString:@"59秒前"], @"");
}

- (void)test1MinutesAgo{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2019-12-14 10:59:00"];
    NSAssert([timeString isEqualToString:@"1分钟前"], @"");
}

- (void)test24MinutesAgo{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2019-12-14 10:36:00"];
    NSAssert([timeString isEqualToString:@"24分钟前"], @"");
}

- (void)test1HoursAgo{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2019-12-14 09:36:00"];
    NSAssert([timeString isEqualToString:@"1小时前"], @"");
}

- (void)test1DayAgo{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2019-12-13 09:36:00"];
    NSAssert([timeString isEqualToString:@"1天前"], @"");
}

//整一天前,边界
- (void)test1DayAgo2{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2019-12-13 11:00:00"];
    NSAssert([timeString isEqualToString:@"1天前"], @"");
}

//整一月前,边界
- (void)test1MonthAgo{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2019-11-14 11:00:00"];
    NSAssert([timeString isEqualToString:@"1月前"], @"");
}

- (void)test1MonthAgo2{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2019-11-13 11:00:00"];
    NSAssert([timeString isEqualToString:@"1月前"], @"");
}

- (void)test3MonthAgo{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2019-09-13 11:00:00"];
    NSAssert([timeString isEqualToString:@"3月前"], @"");
}

//整一年前,边界
- (void)test1YearsAgo{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2018-11-14 11:00:00"];
    NSAssert([timeString isEqualToString:@"1年前"], @"");
}

- (void)test1YearsAgo2{
    NSString * timeString = [self distanceUpLoadTimeWith:@"2018-11-13 11:00:00"];
    NSAssert([timeString isEqualToString:@"1年前"], @"");
}

- (NSString *)distanceUpLoadTimeWith:(NSString *)timeString{
//    NSDate *nowDate = [NSDate date];
    //模拟一个固定的时间点
    NSDate *nowDate = [self dateFromString:@"2019-12-14 11:00:00"];
    NSDate * upLoadTime = [self dateFromString:timeString];
    
    NSTimeInterval interval = [nowDate timeIntervalSinceDate:upLoadTime];

    NSAssert(interval>0, @"时间必须是正的");
    
    NSInteger y = interval/(60*60*24*30*12);
    NSInteger months = interval/(60*60*24*30);
    NSInteger d = interval/(60*60*24);
    NSInteger h = interval/(60*60);
    NSInteger minutes = interval/60;
    NSInteger s = (long long)interval%60;
    
    NSString * distanceString;
    if (y>0) {
        distanceString = [NSString stringWithFormat:@"%ld年前",(long)y];
    }else if (months>0) {
        distanceString = [NSString stringWithFormat:@"%ld月前",(long)months];
    }else if (d>0) {
        distanceString = [NSString stringWithFormat:@"%ld天前",(long)d];
    }else if (h>0) {
        distanceString = [NSString stringWithFormat:@"%ld小时前",(long)h];
    }else if (minutes>0) {
        distanceString = [NSString stringWithFormat:@"%ld分钟前",(long)minutes];
    }else{
        distanceString = [NSString stringWithFormat:@"%ld秒前",(long)s];
    }
    
    return distanceString;
}

- (NSDate *)dateFromString:(NSString *)dateString{
    
    if (!dateString) {
        return nil;
    }
    NSDateFormatter *dateFormatter = nil;
    if (dateFormatter == nil) {
        dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setLocale:[NSLocale currentLocale]];
        [dateFormatter setDateFormat: @"yyyy-MM-dd HH:mm:ss"];
    }
    
    return [dateFormatter dateFromString:dateString];
}

第二个：从数组中选中当前的index,index-1,index+1的单元测试，用于列表浏览图片时展示当前和前后三张。包括本身只有一条数据，前后边界。如果后续要改成4个或5个，也是非常实用。

- (void)testArrayCount1Index0{
    NSArray * array = @[@(1)];
    [self indexprePostArrayWithArray:array index:0];
}

- (void)testArrayCount2Index0{
    NSArray * array = @[@(1),@(2)];
    [self indexprePostArrayWithArray:array index:0];
}

- (void)testArrayCount2Index1{
    NSArray * array = @[@(1),@(2)];
    [self indexprePostArrayWithArray:array index:1];
}

- (void)testArrayCount3Index0{
    NSArray * array = @[@(1),@(2),@(3)];
    [self indexprePostArrayWithArray:array index:0];
}

- (void)testArrayCount3Index1{
    NSArray * array = @[@(1),@(2),@(3)];
    [self indexprePostArrayWithArray:array index:1];
}

- (void)testArrayCount3Index2{
    NSArray * array = @[@(1),@(2),@(3)];
    [self indexprePostArrayWithArray:array index:2];
}

/*
 返回index前后narray
 怎么浏览三张,当前这张在中间;保证数组前后不能越界?
 如果是在第0个位置,数量够时,取0,1,2;如果是最后一个位置,取最后一个位置
 扩展:如果是4张，5张呢?算法的扩展性
 */
- (void)indexprePostArrayWithArray:(NSArray *)array index:(NSInteger)index{
    NSAssert(index>=0 && index<array.count, @"index应在数组范围内");
    NSInteger beign = index-1;
    NSInteger end = index+1;
    
    NSMutableArray * resultArray = [NSMutableArray arrayWithCapacity:3];
    
    if (beign<0) {
        end = end-beign;//减去负值
        beign = 0;
        if (end >= array.count) {
            end = array.count - 1;
        }
    }else if(end>=array.count){
        NSInteger absolute = end-(array.count-1);
        beign = beign-absolute;
        end = array.count-1;
        if (beign<0) {
            beign = 0;
        }
    }
    
    NSAssert(beign>=0, @"begin不会小于0");
    NSAssert(end<array.count, @"end不能大于等于count");
    
    for (NSInteger i = beign; i<=end; i++) {
        [resultArray addObject:array[I]];
    }
    if (array.count>=3) {
        NSAssert(resultArray.count == 3, @"应该有3个");
    }else{
        NSAssert(resultArray.count == array.count, @"与数组个数相等");
    }
}