The prototype of extreme wave, named as Kuznetsov-Ma breather solution has been tested in a seakeeping wave tank with different initial wave steepness and water depths. The laboratory observations can be accurately simulated by the high-order spectral model (HOS) if the initial Benjamin-Feir index is not very large, i.e. weak nonlinearity and/or small water depth. Analysis of the results reveals that the maximum wave height in Kuznetsov-Ma breather solution is inclined to be accompanied with a large crest, which can be largely reduced with the decreasing water depth due to the slower modulational process in the limited length of wave tank, regardless of the degree of the initial nonlinearity. It is also observed that in the evolution process the amplitude of carrier wave will decrease sharply and a peak frequency downshifting can be detected. If the evolutionary time scale is long enough, the spectrum will eventually evolve into a continuous one with the energy redistributed in the lower frequency region. For Peregrine breather solution that is a special case of Kuznetsov-Ma solution, it is found that in some cases a specific phase shift of the initial condition can result in a longer evolutionary distance for the wave group to achieve the maximum amplitude, which is larger than that predicted by the theoretical solution.