How do I access the ith column of a NumPy multidimensional array?

Given:

test = np.array([[1, 2], [3, 4], [5, 6]])

test[i] gives the ith row (e.g. [1, 2]). How do I access the ith column? (e.g. [1, 3, 5]). Also, would this be an expensive operation?