Write unit tests for raster_scan.py

[magsol]

Generate a "sample video":

y = np.arange(18).reshape((3, 3, 2))
y = np.swapaxes(y, 0, 2)
y = np.swapaxes(y, 0, 1)

# y is now the same format as our input videos

z = np.arange(18).reshape((3, 6))

# z is now what we want as output if y was our input

Write a small unit test framework to give raster_scan function a video and test its output against a known ground-truth https://docs.python.org/3/library/unittest.html

[magsol]

Done!