arcgis desktop - Calculate the frequency of classes of neighbouring raster cells

I'm struggling with a problem when working with a raster dataset of biotope types:

For each cell I would like to find out the frequency of classes in the adjacent cells, e.g. from the 8 neighbouring cells 3 are of biotope type A, 4 of type B and 1 cell of type C.

I was recommended to try out 'Block Statistics' and work with a moving window, but so without any success.