75 reduce size of testing files

[DSilva27]

No description provided.

[geoffwoollard]

I checked the file sizes and they are all very small.

Since all the tests pass I think this can be merged in now.

One suggestion is to add some documentation in somewhere as to how you made the test data. A list of commands, or some .sh script perhaps?

[DSilva27]

This is just the osf data after fourier downsampling. I have a notebook where I did this, but not sure what would be the best way to add it here.