def format_sum(self, ar, sums, i):
        if i == 0:
            return E.b(ar.get_sum_text())
        if sums[i]:
            return E.b(self.format_value(ar, sums[i]))
        return ''
Test forecast part of ExponentialSmoothing.
dataset/ETHPy150Open lsaffre/lino/lino/modlib/extjs/elems.py/FieldElement.format_sum--crossover with--dataset/ETHPy150Open T-002/pycast/pycast/tests/methodtest.py/ExponentialSmoothingTest.forecasting_test