On Thursday, the 10-member IAEA team was inspecting two reactors at the Ohi nuclear power plant in Fukui prefecture in western Japan.
Passing the test is one of several steps needed to restart dozens of idled nuclear plants.
Only four of Japan's 54 reactors are currently operating, so getting some back on line would help Japan avoid a power crunch.
If none get approval, Japan will be without an operating reactor by the end of April.
The stress tests are meant to assess how well the plants could withstand earthquakes, tsunamis and other extreme events.