The study shows that Johansen's tests may not accurately detect cointegration relationships in certain situations. When there are additional unrelated series in the system or multiple cointegration relationships driven by different shocks, the tests may fail to identify cointegration. This means that using Johansen's tests on systems with both real and nominal series can lead to biased results. To improve accuracy, researchers should test for cointegration based on the smallest system where economic theory suggests cointegration should exist. Failure to do so can result in undetected cointegration between various economic variables like money velocity and interest rates, real estate prices and rents, or GDP and consumption.