Sentiment analysis using sklearn

[qrious]

I am attempting to understand how scikit learn works for sentiment analysis and came across this blog post: 

https://marcobonzanini.wordpress.com/2015/01/19/sentiment-analysis-with-python-and-scikit-learn 

The corresponding code is at this location: 

https://gist.github.com/bonzanini/c9248a239bbab0e0d42e 

My question is while trying to predict, why does the curr_class in Line 44 of the code need a classification (pos or neg) for the test data? After all, am I not trying to predict it? Without any initial value of curr_class, the program has a run time error.

Any help will be greatly appreciated.