Watertightness performances of skylight systems are determined according to EN 12155 and ASTM E 331 standards. During tests, inner face of the specimen is subjected to defined test pressure levels and exterior face of the specimen is sprayed by water with defined amount to supplying continuous water layer on whole exterior area. Inner face of the specimen is checked during the test, whether there is any water leakage. All skylight samples up to 30 m2 can be tested; and the angle of testing unit can be adjusted between 0 and 90 degrees as befitting project applications. Moreover, air permeability (EN 12153 and ASTM E 283) and wind resistance (EN 12179 and ASTM E 330) tests can be run on the same unit as well.