remove NA rows and columns

Hello,

I guess, it's a rather simple thing but I cannot find a short way to reduce a 
matrix, removing all rows and columns having just NA elements.

testmatrix <- matrix(nrow=6, ncol=4)
testmatrix[2:5,2:3] <- seq(2)

 > testmatrix

      [,1] [,2] [,3] [,4]
[1,]   NA   NA   NA   NA
[2,]   NA    1    1   NA
[3,]   NA    2    2   NA
[4,]   NA    1    1   NA
[5,]   NA    2    2   NA
[6,]   NA   NA   NA   NA

the new matrix should look like this (by the way, I don't "know" which rows and 
columns are the one to be deleted...

 > testmatrix

      [,1] [,2]
[1,]   1    1
[2,]   2    2
[3,]   1    1
[4,]   2    2

Ciao,
Antje