Just a few months after Toyota and Tesla Motors announced a collaboration on an electric car, a Tesla spokeswoman says a prototype has already been built and is undergoing testing.

Toyota and Tesla made a big splash in May, announcing Toyota’s planned $50 million investment in the electric car maker and a Tesla takeover of the Nummi plant in Fremont, Calif. On Monday, Bloomberg Businessweek reported that the next steps — to build Toyota electric vehicle prototypes with Tesla power trains — are being undertaken very quickly and quietly.

When reached for details on the Bloomberg report, Khobi Brooklyn, a Tesla spokeswoman, said in an e-mail message that the prototype “is undergoing testing. It will be unveiled to the public later this year.” She declined to comment on specifics but wrote that the companies had signed a development agreement to put together “a high-volume Toyota vehicle with a Tesla electric power train.”

Ms. Brooklyn also passed along a comment from JB Straubel, Tesla’s chief technology officer. “Since our announcement in May, Toyota and Tesla engineering teams have made a lot of progress in a short amount of time and it is exciting to start seeing some initial results,” he said.

Mira Sleilati, a spokeswoman for Toyota Motor North America, also said the company couldn’t confirm the details of the Bloomberg report. “The two companies have teams studying where we might be working together,” she said. “We have not confirmed any particular model. But as we said at the announcement, we have a wide-open view of our possible collaboration in E.V. development and production engineering. ”

According to Bloomberg, Tesla is building electric test versions of the RAV4 and Lexus RX S.U.V.’s, and Toyota will receive them this month. It also said that the goal of the joint development project was an E.V. with a 150-mile range that could be sold for $40,000.

Toyota and Tesla said last spring that they would cooperate on E.V.’s, parts, production systems and engineering support. Tesla will produce its Model S sedan at Nummi, but the large plant could also accommodate a jointly developed Toyota-Tesla vehicle.