(req: express.Request, res: express.Response, next: express.NextFunction) => {
      const draft: Draft<ResponseDraft> = res.locals.draft

      res.locals.monthlyIncomeAmount = draft.document.statementOfMeans ? CalculateMonthlyIncomeExpense.calculateTotalAmount(
        IncomeExpenseSources.fromMonthlyIncomeFormModel(draft.document.statementOfMeans.monthlyIncome).incomeExpenseSources
      ) : 0
      res.locals.monthlyExpensesAmount = draft.document.statementOfMeans ? CalculateMonthlyIncomeExpense.calculateTotalAmount(
        IncomeExpenseSources.fromMonthlyExpensesFormModel(draft.document.statementOfMeans.monthlyExpenses).incomeExpenseSources
      ) : 0
      next()
    }

 it('should return a new instance initialised with set fields from object parameter provided', () => {
   expect(IncomeExpenseSources.fromObject(SAMPLE_INCOME_EXPENSE_SOURCES_FROM_OBJECT)).to.deep.equal(
     new IncomeExpenseSources(
       [
         {
           'amount': 100,
           'schedule': IncomeExpenseSchedule.MONTH
         }
       ]
     )
   )
 })

function calculateTotalMonthlyIncomeExpense (model: MonthlyIncome): number {
  if (!model) {
    return undefined
  }
  const incomeExpenseSources = IncomeExpenseSources.fromMonthlyIncomeFormModel(model)

  if (!isValid(incomeExpenseSources)) {
    return undefined
  }

  return CalculateMonthlyIncomeExpense.calculateTotalAmount(
    incomeExpenseSources.incomeExpenseSources
  )
}

  .post(Paths.totalIncomeOrExpensesCalculation.uri, async (req: express.Request, res: express.Response) => {
    try {
      const incomeExpenseSources: IncomeExpenseSources = IncomeExpenseSources.fromObject(req.body)

      const validator: Validator = new Validator()
      const error: ValidationError[] = await validator.validate(incomeExpenseSources)
      if (error.length > 0) {
        return res.status(HttpStatus.UNPROCESSABLE_ENTITY).send(error)
      }

      const totalMonthlyIncomeExpense = CalculateMonthlyIncomeExpense
        .calculateTotalAmount(incomeExpenseSources.incomeExpenseSources)
      return res.status(HttpStatus.OK).json({
        totalMonthlyIncomeExpense: totalMonthlyIncomeExpense
      })
    } catch (err) {
      return res.status(HttpStatus.UNPROCESSABLE_ENTITY).send(err)
    }
  })

 expect(() => IncomeExpenseSources.fromObject({ incomeExpenseSources: 'not an array' })).to.throw(Error, 'Invalid value: missing array')