#NEWLINE# def test_collect_D_0( ) : #NEWLINE# #INDENT# D = Derivative #NEWLINE# f = Function ( 'f' ) #NEWLINE# ( x , a , b ) = symbols ( 'x,a,b' ) #NEWLINE# fxx = D ( f ( x ) , x , x ) #NEWLINE# assert ( collect ( ( ( a * fxx ) + ( b * fxx ) ) , fxx ) == ( ( a + b ) * fxx ) )