Fix test associated with SobolevSegmenter extension.

See https://github.com/anry123/SobolevSegmenter/compare/006f4278159cd3a6515bab3fafec83546e13ffe7...c895f96
Merge pull request #271 from jcfr/update-SobolevSegmenter

Fix test associated with SobolevSegmenter extension.