add assert raises in the test_retain_graph UT. (#25983)

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

@@ -20,7 +20,7 @@ import unittest
 paddle.disable_static()
 SEED = 2020
 np.random.seed(SEED)
-fluid.default_main_program().random_seed = SEED
+paddle.manual_seed(SEED)
 
 
 class Generator(fluid.dygraph.Layer):
@@ -90,7 +90,7 @@ class TestRetainGraph(unittest.TestCase):
         else:
             return 0.0, None
 
-    def test_retain(self):
+    def run_retain(self, need_retain):
         g = Generator()
         d = Discriminator()
 
@@ -117,7 +117,7 @@ class TestRetainGraph(unittest.TestCase):
             d, realA, fakeB, lambda_gp=10.0)
         loss_d = gan_criterion(G_pred_fake, false_target) + G_gradient_penalty
 
-        loss_d.backward(retain_graph=True)
+        loss_d.backward(retain_graph=need_retain)
         optim_d.minimize(loss_d)
 
         optim_g.clear_gradients()
@@ -130,6 +130,11 @@ class TestRetainGraph(unittest.TestCase):
         loss_g.backward()
         optim_g.minimize(loss_g)
 
+    def test_retain(self):
+        self.run_retain(need_retain=True)
+        self.assertRaises(
+            fluid.core.EnforceNotMet, self.run_retain, need_retain=False)
+
 
 if __name__ == '__main__':
     unittest.main()