def METHOD_NAME(centers):
    """Check that none of the spheres in the packed configuration overlap."""
    # Create KD tree for quick nearest neighbor search
    tree = scipy.spatial.cKDTree(centers)
    # Find distance to nearest neighbor for all spheres
    d = tree.query(centers, k=2)[0]
    # Get the smallest distance between any two spheres
    d_min = min(d[:, 1])
    assert d_min > 2*_RADIUS or d_min == pytest.approx(2*_RADIUS)