### Question:
InMemoryServiceInstanceStateRepository implements ServiceInstanceStateRepository { @Override public Mono<ServiceInstanceState> removeState(String serviceInstanceId) { return containsState(serviceInstanceId) .flatMap(contains -> Mono.defer(() -> { if (contains) { return Mono.fromCallable(() -> this.states.remove(serviceInstanceId)); } else { return Mono.error(new IllegalArgumentException("Unknown service instance ID " + serviceInstanceId)); } })); }  @Override Mono<ServiceInstanceState> saveState(String serviceInstanceId, OperationState state, String description); @Override Mono<ServiceInstanceState> getState(String serviceInstanceId); @Override Mono<ServiceInstanceState> removeState(String serviceInstanceId);  }### Answer:
@Test void removeWithUnknownServiceInstanceId() { StepVerifier.create(stateRepository.removeState("foo")) .expectError(IllegalArgumentException.class) .verify(); }