### Question:
BatchedMeanSmoother { public double currentAverage() { return total / totalCount; } BatchedMeanSmoother(int w); double currentAverage(); void addBatch(int n, double val);  }### Answer:
@Test public void testEmpty() { BatchedMeanSmoother smooth = new BatchedMeanSmoother(10); assertThat(smooth.currentAverage(), notANumber()); }