ComputeRange.java

 static class MinMax {
        public DataPoint<Double> min;
        public DataPoint<Double> max;
    }

    @Test
    public void findRange() 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);

        Double range = metricsService.findGaugeData("t1", new MetricId("m1"), start.getMillis(),
                end.plusSeconds(10).getMillis())
                .reduce(new MinMax(), (MinMax minAndMax, DataPoint<Double> dataPoint) -> {
                    if (minAndMax.min == null) {
                        minAndMax.min = dataPoint;
                        minAndMax.max = dataPoint;
                    } else {
                        if (dataPoint.getValue() < minAndMax.min.getValue()) {
                            minAndMax.min = dataPoint;
                        }
                        if (dataPoint.getValue() > minAndMax.max.getValue()) {
                            minAndMax.max = dataPoint;
                        }
                    }
                    return minAndMax;
                })
                .map((MinMax minAndMax) -> minAndMax.max.getValue() - minAndMax.min.getValue())
                .toBlocking().last();

        assertEquals(range, 4.4 - 1.1, "The range is wrong");
    }