DETROIT/SAN FRANCISCO (Reuters) - Tesla Inc has told suppliers it planned to begin test-building its Model 3 sedans on Feb. 20, according to people familiar with the matter, a move that could allay concerns about the company meeting its target to start production in July. The sources did not know how many of the highly anticipated vehicles Tesla aimed to build in February, but it would likely be a small number to test the assembly system and the quality of vehicle parts. Tesla Chief Executive Elon Musk last year told investors and more than 370,000 customers who put deposits down for a Model 3 that he intended to start building the cars in July 2017.