title: Flux:How to test empty Flux
body: <p>Is there a way to use ArgumentCapture for Flux?</p>
  
  <p>I want to mock a service where the input parameters (flux) are created during the process:</p>
  
  <pre><code>Flux&lt;A&gt; fluxa = createFluxA();
  Flux&lt;B&gt; fluxb = createFluxB()
  ...
  return service.createMono(fluxa,fluxb)
  </code></pre>
  
  <p>My Unit Test: </p>
  
  <pre><code>AObject aobject = mock(AObject.class);
  when(service.createMono(any(), any()).thenReturn(Mono.just(aobject));
  
  ...
  StepVerifer...
  </code></pre>
  
  <p>The Unit Test works only if I use the matcher any(). If fluxB should be a empty Flux how can I test this? eq(Flux.empty()) does not work because Flux has no equal function</p>
  
  <p>Thx in advance</p>