### Question:
MeterSdk implements Meter { @Override public LongSumObserverSdk.Builder longSumObserverBuilder(String name) { return new LongSumObserverSdk.Builder(name, meterProviderSharedState, meterSharedState, this); } MeterSdk(
      MeterProviderSharedState meterProviderSharedState,
      InstrumentationLibraryInfo instrumentationLibraryInfo,
      ViewRegistry viewRegistry); @Override DoubleCounterSdk.Builder doubleCounterBuilder(String name); @Override LongCounterSdk.Builder longCounterBuilder(String name); @Override DoubleUpDownCounterSdk.Builder doubleUpDownCounterBuilder(String name); @Override LongUpDownCounterSdk.Builder longUpDownCounterBuilder(String name); @Override DoubleValueRecorderSdk.Builder doubleValueRecorderBuilder(String name); @Override LongValueRecorderSdk.Builder longValueRecorderBuilder(String name); @Override DoubleSumObserverSdk.Builder doubleSumObserverBuilder(String name); @Override LongSumObserverSdk.Builder longSumObserverBuilder(String name); @Override DoubleUpDownSumObserverSdk.Builder doubleUpDownSumObserverBuilder(String name); @Override LongUpDownSumObserverSdk.Builder longUpDownSumObserverBuilder(String name); @Override DoubleValueObserverSdk.Builder doubleValueObserverBuilder(String name); @Override LongValueObserverSdk.Builder longValueObserverBuilder(String name); @Override BatchRecorderSdk newBatchRecorder(String... keyValuePairs);  }### Answer:
@Test void testLongSumObserver() { LongSumObserverSdk longObserver = testSdk .longSumObserverBuilder("testLongSumObserver") .setDescription("My very own counter") .setUnit("metric tonnes") .build(); assertThat(longObserver).isNotNull(); assertThat( testSdk .longSumObserverBuilder("testLongSumObserver") .setDescription("My very own counter") .setUnit("metric tonnes") .build()) .isSameAs(longObserver); assertThrows( IllegalArgumentException.class, () -> testSdk.longSumObserverBuilder("testLongSumObserver").build(), "Instrument with same name and different descriptor already created."); assertThrows( IllegalArgumentException.class, () -> testSdk.longSumObserverBuilder("testLongSumObserver".toUpperCase()).build(), "Instrument with same name and different descriptor already created."); }