def METHOD_NAME(self):
    """Prepare tests."""
    shape = (3, 2, 2)
    self.z = shape[0]
    data = np.arange(np.prod(shape)).reshape(shape)
    cubes = iris.cube.CubeList()
    # Create first realization cube.
    cube = _make_cube(data)
    coord = iris.coords.DimCoord(0, standard_name='realization')
    cube.add_aux_coord(coord)
    cubes.append(cube)
    # Create second realization cube.
    cube = _make_cube(data + np.prod(shape))
    coord = iris.coords.DimCoord(1, standard_name='realization')
    cube.add_aux_coord(coord)
    cubes.append(cube)
    # Create a 4d synthetic test cube.
    self.cube = cubes.merge_cube()
    coord = self.cube.coord(axis='z', dim_coords=True)
    self.shape = list(self.cube.shape)
    [self.z_dim] = self.cube.coord_dims(coord)