Add more tests to cover num2words/base.py
Add more tests to cover num2words/base.py

Fix:
 - https://github.com/savoirfairelinux/num2words/issues/125

Signed-off-by: William José Moreno Reyes <59194fa0d047763d7146e35e43bdf7a83454435e@gmail.com>

savoirfairelinux/num2words