Examples of correct and incorrect pinyin
An idea coming from here suggests to take the HSK vocabulary list annotated with pinyin and put the words list to Google translate. The post's author found 11% of words incorrectly converted for HSK level 1-3 words.
The issue is that the official HSK website provides only a words-list without pinyin in an excel format. However, you can find respectively here and here words-lists annotated with pinyin in a pdf or on a website which you can later programmatically convert in a suitable format.
EDIT, in comments:

HSK wordlist with pinyin in tab-separated values