This weekend Iran conducted a ballistic missile test, per an AP report. According to Fox, the test took place by Semnan to the East of Tehran and exploded after 600 miles of flight. Although Sean Spicer dodged questions about it at the White House press briefing today, he told the press Trump was informed of the test over the weekend and the U.S. is studying the details.
Did Iran actually break any resolutions? The UN Security Council Resolution 2231 tells all in Annex B, paragraph 3:
Iran is called upon not to undertake any activity related to ballistic missiles designed to be capable of delivering nuclear weapons, including launches using such ballistic missile technology. — UN Security Council Resolution 2231
Iran claims it did not violate the resolution since these ballistic missiles are not meant to carry nuclear warheads.
A test for Trump: This is not the first time since the resolution passed that Iran has conducted tests, but this is the first action Iran has taken during Trump's presidency.