source: class CircuitBreakerImplTest {
  
      private CircuitBreakerImpl<String> cbSpy;
  
      @Test
      public void isEventACircuitBreakerFailure_returns_whatever_breakingEventStrategy_returns() {
  
target:         // given
          BreakingEventStrategy<String> falseDecider = theString -> false;
          Whitebox.setInternalState(cbSpy, "breakingEventStrategy", falseDecider);
  
          // expect
          assertThat(cbSpy.isEventACircuitBreakerFailure("foo")).isFalse();
  
          // and given
          BreakingEventStrategy<String> trueDecider = theString -> true;
          Whitebox.setInternalState(cbSpy, "breakingEventStrategy", trueDecider);
  
          // expect
          assertThat(cbSpy.isEventACircuitBreakerFailure("foo")).isTrue();
      }
  
  }