Refine trunc uinttest logic (#43016)

* refine trunc uinttest

* refine unittest

* refine ut

* refine fp64 grad check

python/paddle/fluid/tests/unittests/test_trunc_op.py

@@ -30,7 +30,7 @@ class TestTruncOp(OpTest):
     def setUp(self):
         self.op_type = "trunc"
         self.python_api = paddle.trunc
-        self.dtype = np.float64
+        self.init_dtype_type()
         np.random.seed(2021)
         self.inputs = {'X': np.random.random((20, 20)).astype(self.dtype)}
         self.outputs = {'Out': (np.trunc(self.inputs['X']))}
@@ -48,11 +48,19 @@ class TestTruncOp(OpTest):
 class TestFloatTruncOp(TestTruncOp):
     def init_dtype_type(self):
         self.dtype = np.float32
+        self.__class__.exist_fp64_check_grad = True
+
+    def test_check_grad(self):
+        pass
 
 
 class TestIntTruncOp(TestTruncOp):
     def init_dtype_type(self):
         self.dtype = np.int32
+        self.__class__.exist_fp64_check_grad = True
+
+    def test_check_grad(self):
+        pass
 
 
 class TestTruncAPI(unittest.TestCase):