Would it be possible to divide the test into smaller segments? The student could complete one part of the test, complete other tasks and later complete the rest of the test. Or is it possible to reduce the number of problems on the test until the student begins to show some success and gain some confidence? The number of problems on the test could gradually be increased.
Maybe the student could be given a practice test that is similar to the test. Another option might be to teach very specific test taking strategies. Teach the student how to read and reread the directions, take one problem at a time, complete the easy problems first and highlight the important words of the story problem, etc.