function validTime(str) {
    if (!str.includes(':')) {
        throw 'input must be in HH:MM format'
    }
    
    temp = str.split(':');
    hour = temp[0];
    min = temp[1];
    
    if (hour > 23 || hour < 0) {
        return false;
    } else if (min > 59 || min < 0) {
        return false;
    }
    
    return true;
}



/**
* Test Suite 
*/
describe('validTime()', () => {
    it('returns true for valid time', () => {
        // arrange
        const str = '13:58';
        
        // act
        const result = validTime(str);

        // log
        console.log("result 1: ", result);
        
        // assert
        expect(result).toBe(true);
    });

    it('returns false when invalid hours', () => {
        // arrange
        const str = '25:51';
        
        // act
        const result = validTime(str);

        // log
        console.log("result 1: ", result);
        
        // assert
        expect(result).toBe(false);
    });

    it('returns false when invalid minutes', () => {
        // arrange
        const str = '02:76';
        
        // act
        const result = validTime(str);

        // log
        console.log("result 1: ", result);
        
        // assert
        expect(result).toBe(false);
    });
    
    it('throws an error when input is invalid format', () => {
       const str = '2310';
       const error = 'input must be in HH:MM format';
       expect(function() {
           validTime(str);
           }).toThrow(error); 
    });
});