It has been recently claimed that dark energy can be (and has been) observed in laboratory experiments by measuring the power spectrum SI (ω) of the noise current in a resistively shunted Josephson junction and that in new dedicated experiments, which will soon test a higher frequency range, SI (ω) should show a deviation from the linear rising observed in the lower frequency region because higher frequencies should not contribute to dark energy. Based on previous work on theoretical aspects of the fluctuation-dissipation theorem, we carefully investigate these issues and show that these claims are based on a misunderstanding of the physical origin of the spectral function SI(ω). According to our analysis, dark energy has never been (and will never be) observed in Josephson junctions experiments. We also predict that no deviation from the linear rising behavior of SI(ω) will be observed in forthcoming experiments. Our findings provide new (we believe definite) arguments which strongly support previous criticisms.