code: @Override
      public void contains(Map<String, Object> expectedPairs) {
          assertTrue("Expected to find " + Reporter.formatKeyPair(expectedPairs), checkContains(expectedPairs));
      }
docs: Asserts the actual response json payload contains each of the pair
  values provided, and writes that to the output file. If this fails, the code will
  immediately exit, and record the error.
  
  @param expectedPairs a hashmap with string key value pairs expected in the json
  response