test.java

 @Test
    public void findAvg() throws Exception {
        DateTime start = now().minusMinutes(30);
        DateTime end = start.plusMinutes(20);
        String tenantId = "t1";

        metricsService.createTenant(new Tenant(tenantId)).toBlocking().lastOrDefault(null);

        Metric<Double> m1 = new Metric<>(tenantId, GAUGE, new MetricId("m1"), asList(
                new DataPoint<>(start.getMillis(), 1.1),
                new DataPoint<>(start.plusMinutes(2).getMillis(), 2.2),
                new DataPoint<>(start.plusMinutes(4).getMillis(), 3.3),
                new DataPoint<>(end.getMillis(), 4.4)
        ));

        Observable<Void> insertObservable = metricsService.addGaugeData(Observable.just(m1));
        insertObservable.toBlocking().lastOrDefault(null);

        Observable<DataPoint<Double>> observable = metricsService.findGaugeData("t1", new MetricId("m1"),
                start.getMillis(), end.getMillis());
//        Double avg = MathObservable.averageDouble(observable.map(DataPoint::getValue)).toBlocking().last();
        List<Double> values = toList(observable.map(DataPoint::getValue));

        double sum = 0.0;
        for (double value : values) {
            sum += value;
        }
        double avg = sum / values.size();

        assertEquals(avg, (1.1 + 2.2 + 3.3 + 4.4) / 4, "The data does not match the expected values");
    }