function adjacentElementsProduct(nums) {
    //  write code here.
    return nums.reduce((largest, num, index, array) => {
      if (index > 0) {
          let test = num * array[index - 1]
          return (test > largest) ? test : largest
      }  
    })
}

/**
* Test Suite 
*/
describe('adjacentElementsProduct()', () => {
    it('returns largest product of adjacent values', () => {
        // arrange
        const nums = [3, 6, -2, -5, 7, 3];
        
        // act
        const result = adjacentElementsProduct(nums);

        // log
        console.log("result: ", result);
        
        // assert
        expect(result).toBe(21);
    });
});