title: DynamoDB javascript SDK batchWriteItem doesn't complete unless I increase write capacity
body: <p>I'm running a series of unit tests (node.js 4.x, aws-sdk, mocha) which load data into a table before each test then clears the table after the test.</p>
  
  <p>I have two tests that are failing because of a <code>ConditionExpression</code> which triggers a <code>ConditionCheckFailedException</code>. But if I increase the read/write capacity they tests pass.</p>
  
  <p>It's my understanding that the SDK handles throttling exceptions and retries them for you so why wouldn't my tests just run slower and pass? Instead it seems as though the tests fail to complete the <code>scan</code> -> <code>batchWriteItem</code> process and so there are records still left in the table when a new tests starts.</p>
  
  <p>I'm told by team members that they've seen similar problems and they just increased the throughput to fix the problem. This doesn't sit right with me. Either I'm doing something wrong and there's a race condition with my tests or there should be a pattern I can implement to make sure that my operations complete when being throttled? I should be able to use throttling metrics to inform when I need to increase throughput but I should still be able to keep retrying until I run out of memory.</p>
  
  <p>Has anyone else run into this and what have you done to handle the problem?</p>