[new-exec] refine ut (#38798)

python/paddle/fluid/tests/unittests/interpreter/test_standalone_executor.py

@@ -32,18 +32,16 @@ class LinearTestCase(unittest.TestCase):
         self.place.set_place(place)
 
     def build_program(self):
+        startup_program = paddle.static.Program()
+        main_program = paddle.static.Program()
+        with paddle.static.program_guard(main_program, startup_program):
             a = paddle.static.data(name="a", shape=[2, 2], dtype='float32')
             b = paddle.ones([2, 2]) * 2
             t = paddle.static.nn.fc(a, 2)
             c = t + b
 
-        main_program = paddle.fluid.default_main_program()
-        startup_program = paddle.fluid.default_startup_program()
-
         return startup_program, main_program, c
 
-        return standaloneexecutor, c
-
     def test_interp_base(self):
         startup_program, main_program, c = self.build_program()
         standaloneexecutor = StandaloneExecutor(