##To run tests
$ npm install$ npm run test
##To run exponential backoff
$ node backoff/backoff.js
###Question 1
The issue here was that if doThing erred, then the callback was called twice as the function did not return.
I implemented doThing to err and I added the return statement.
I have implemented a test to check that the callback is only called once.
###Question 2
The issue here was that callOneService and callTwoService are asynchronous calls and were not called in sequence.
I changed the code to call the callbacks in sequence and have created a test
###Question 3
I have implemented the exponentialBack function.