add a more thorough test for TELEMAC

[tomsail]

I am writing this to not forget it:

Before merging the telemac branch, I'd be nice to

• add a max value test in test_telemac.py

[tomsail]

This issue should have be addressed with 5c00dcc
We can close when merging #176

[pmav99]

For the record, you could add a line in the commit message with the text fixes #177 and it would be closed automatically upon merge.

[tomsail]

After discussion, a more thorough assertion for TELEMAC tests needs to be implemented