@Override
    public long read() {
        return gaugeSource.read();
    }
@Test
    public void whenLongProbe() {
        metricsRegistry.registerStaticProbe(this, "foo", MANDATORY, (LongProbeFunction) o -> 10);

        LongGauge gauge = metricsRegistry.newLongGauge("foo");
        assertEquals(10, gauge.read());
    }