This doesn't prove a lot since the Arduinos tend to have I2C pull-ups on-board, but Particles haven't.
So if it were about missing pull-ups that test would not make you any wiser.
But there are some threads already about HTU21 and some of them are marked as solved, so you might find something there (even in the ones about Adafruit boards)
Search results for 'htu21 solved' - Particle
You could also check if the I2C address in the library is correct by use of the i2c_scanner sketch in this thread
Photon flashed once, now can't flash again