1.js

function addTwoNumbers(numberOne, numberTwo){}

2.js

describe( 'Adding two number', () => {
	it( 'works with postive numbers', () => {
		expect( addTwoNumbers(1,2) ).toBe(3);
	});
	it( 'works with a negative number', () =>{
		expect( addTwoNumbers(-1,2) ).toBe(1);

	});
});

3.js

function addTwoNumbers(numberOne, numberTwo){
	return numberOne + numberTwo;
}

4.js

describe( 'Adding two number', () => {
	it( 'works with postive numbers', () => {
		expect( addTwoNumbers(1,2) ).toBe(3);
	});
	it( 'works with a negative number', () =>{
		expect( addTwoNumbers(-1,2) ).toBe(1);
	});
	
	it( 'rounds when rounding argument is passed', () => {
		expect( addTwoNumbers( 1, 2.555555, 2 ) ).toBe( 3.55 );
	});

	it( 'Does not round by default', () => {
		expect( addTwoNumbers( 1, 2.555555 ) ).toBe( 3.555555 );
	});
});

5.js

function addTwoNumbers(numberOne, numberTwo, precision = null ){
	let sum = numberOne + numberTwo;
	if( precision ){
		sum = Number.parseFloat(sum).precision(4);
	}
	return sum;
}