In the 1950's, Wing Chun was tested extensively in Hong Kong against all the other major styles of combat. It was mostly through the documented fights of master Wong Shun Leung and master Wong Kiu that Wing Chun got its reputation of being an effective combat art.
These individuals first competed against the students of various styles. Later, they competed against the masters themselves. The success of Wing Chun caused a sharp rise in the number of students who wanted to study Wing Chun. It was during these fights that Bruce Lee got attracted to Wing Chun.
Today, Wing Chun is also successful in tournament competition around the world. One female student of master Wong Shun Leung became the all Asian martial arts champion (against all styles). Another female student descending from master Wong Kiu received similar status in Holland.
Recently, we heard news of Wing Chun's success against Thai boxing, but details are still sketchy. Apparently, there were three rounds. The first round was won by the Wing Chun practitioner who used a Bong leg followed by ruffle punches. Although the Wing Chun practitioner technically won, he did so at the price of a splintered leg.
Wing Chun seems to fare quite well in Dutch tournements against Tae Kwon-Do. We have little information on these tournaments at this point.
We have also heard that two Wing Chun practitioners who competed against Karate in Japan, received broken arms from trying to block roundhouse kicks using the Gan sau.
We believe these students violated fundamental principles of Wing Chun by clashing with a stronger force. In all probability they underestimated their opponent or they were not experienced fighters.
The Wing Chun Kung Fu Digital Library