On February 2, 2019, about 1700 eastern standard time, a Cessna 150F, N6789F, was substantially damaged when it was involved in an accident near Knotts Island, North Carolina. The commercial pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he was performing a post-maintenance test flight. Before departure, the pilot reviewed the logbooks and conducted a pre-flight inspection. He said that the airplane had about 22 gallons of usable fuel on board before takeoff. After departure, the pilot remained in the airport traffic pattern and conducted several landings, then departed the traffic pattern and flew 10 miles to the south, where he conducted maneuvers. After about 30 minutes of flight maneuvers, he turned east toward the Outer Banks Barrier Islands. While en route, the pilot stated that he experienced the instruments “turning off and on.” He made a turn back toward the departure airport, and shortly after, the electrical system failed followed by a total loss of engine power. The pilot attempted to restart the engine but was unsuccessful, and conducted a forced landing in a marsh. The pilot exited the airplane and contacted the local authorities. According to the operator, the pilot was advised to remain in the traffic pattern of the local airport, considering how much maintenance was recently performed. The mechanic who performed the maintenance watched as the pilot performed 30 minutes of engine runs, taxiing, and operational tests on the ground prior to the test flight. The pilot made a series of touch-and-go landings, short field landings, and low passes before departing the traffic pattern. An examination of the airplane by a Federal Aviation Administration inspector revealed that the airplane came to rest inverted with the nose landing gear partially detached from the engine mount. The airplane was recovered, and flight control continuity was established. Examination of the engine did not reveal any anomalies that would have prevented normal operation. About 1 cup of fuel was drained from the fuel system. The fuel was “yellowish” in color and absent of any visible contamination. The fuel selector was found in the ON position. Both fuel caps were inspected, and the fuel cap gaskets were intact. Both wing fuel tanks were empty of fuel, and there were no signs of fuel leakage on the airframe or at the accident site. A review of the fueling records revealed that the airplane was fueled with 15.8 gallons of 100LL aviation fuel earlier on the day of the accident.