When running the tests I get an error in this line. The reason seems to be that `make_montage()` is called with an image that has the same color in every pixel (hence ndimage labeling fails). Strangely such an error does not happen when I run the script below which runs the same commands. Is this related to how these scripts are run during testing?

```python
import os

import numpy as np

from mayavi import mlab
import surfer


data_dir = os.path.join(os.path.split(surfer.__file__)[0], '..',
                        'examples', 'example_data')


mlab.options.backend = 'auto'

brain = surfer.Brain('fsaverage', 'lh', 'inflated')
stc_fname = os.path.join(data_dir, 'meg_source_estimate-lh.stc')
stc = surfer.io.read_stc(stc_fname)
data = stc['data']
time = 1e3 * np.linspace(stc['tmin'],
                         stc['tmin'] + data.shape[1] * stc['tstep'],
                         data.shape[1])

brain.add_data(data, colormap='hot', vertices=stc['vertices'],
               smoothing_steps=10, time=time, time_label='time=%0.2f ms')
brain.scale_data_colormap(fmin=13, fmid=18, fmax=22, transparent=True)



brain.save_movie('test', montage=['lat', 'med'], orientation='v')

brain.close()
```