HCRVolume * __block volume = nil;

[[self.client fetchVolumeWithID:@"L9fpff1b4kwC"] subscribeNext:^(id x) {
    volume = x;
}];
    
TGRAssertEventually(volume != nil, @"should complete with a response");
XCTAssertTrue([volume isKindOfClass:HCRVolume.class], @"should return a single volume");