Section 46A. Said college and said institute may make, under such regulations as their respective boards of trustees may from time to time prescribe, tests, comparative or otherwise, of new and useful improvements in textile machinery or of apparatus, dyes, compounds, processes, methods or means, directly or indirectly relating to the manufacture of textiles or to the machinery, tools, appliances and materials used in connection therewith. The person for whom any such test is made shall pay therefor on account of the commonwealth a sum not less than the actual cost thereof, including a reasonable amount for overhead expense. No such test shall be undertaken by said college or said institute which in the opinion of the trustees will be likely to interfere with the regular, efficient and proper exercise of school functions. In the making of such tests preference shall be given to citizens of, and to corporations organized under the laws of, the commonwealth.