@Override
    public long read() {
        return gaugeSource.read();
    }
@Test
    public void whenDoubleProbe() {
        metricsRegistry.registerStaticProbe(this, "foo", MANDATORY,
                (DoubleProbeFunction<LongGaugeImplTest>) source -> 10);

        LongGauge gauge = metricsRegistry.newLongGauge("foo");

        long actual = gauge.read();

        assertEquals(10, actual);
    }