TST: improve test coverage for swt2, swtn, swt_axis
TST: improve test coverage for swt2, swtn, swt_axis

rgommers/pywt,grlee77/pywt,rgommers/pywt,eriol/pywt,eriol/pywt,michelp/pywt,PyWavelets/pywt,rgommers/pywt,michelp/pywt,eriol/pywt,rgommers/pywt,michelp/pywt,PyWavelets/pywt,grlee77/pywt