Fix Python IndexError of case2-3 (#49986)

* add shape check for fused_multi_head_attention

* use raise for coverage test

* add unittest

* remove unnecessary pass

* add unittest

Author: RedContritio

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

@@ -192,5 +192,17 @@ def set_configs(self):
         self.normalize_before = True
 
 
+class TestFusedAttentionAPIError(unittest.TestCase):
+    def test_invalid_x_rank(self):
+        def test_x_rank_1():
+            with paddle.fluid.dygraph.guard():
+                layer = FusedMultiHeadAttention(embed_dim=1, num_heads=1)
+                array = np.array([1.9], dtype=np.float32)
+                x = paddle.to_tensor(np.reshape(array, [1]), dtype='float32')
+                out = layer(x)
+
+        self.assertRaises(ValueError, test_x_rank_1)
+
+
 if __name__ == "__main__":
     unittest.main()

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

@@ -1051,5 +1051,31 @@ def test_fused_multi_transformer_op(self):
             )
 
 
+class TestFusedMultiAttentionAPIError(unittest.TestCase):
+    def test_errors(self):
+        def test_invalid_input_dim():
+            array = np.array([1.9], dtype=np.float32)
+            x = paddle.to_tensor(np.reshape(array, [1]), dtype='float32')
+            layer = paddle.incubate.nn.FusedMultiHeadAttention(
+                embed_dim=1, num_heads=1
+            )
+            out = layer(x)
+
+        self.assertRaises(ValueError, test_invalid_input_dim)
+
+
+class TestFusedMultiTransformerAPIError(unittest.TestCase):
+    def test_errors(self):
+        def test_invalid_input_dim():
+            array = np.array([], dtype=np.float32)
+            x = paddle.to_tensor(np.reshape(array, [0]), dtype='int32')
+            layer = paddle.incubate.nn.FusedTransformerEncoderLayer(
+                108, 108, 108, 0.0, 'relu'
+            )
+            out = layer(x)
+
+        self.assertRaises(ValueError, test_invalid_input_dim)
+
+
 if __name__ == "__main__":
     unittest.main()

python/paddle/incubate/nn/functional/fused_transformer.py

@@ -615,6 +615,11 @@ def fused_multi_head_attention(
         'downgrade_in_infer' if mode == 'downscale_in_infer' else mode
     )  # semantic transfer
 
+    if x.ndim != 3:
+        raise ValueError(
+            f"The rank of the x should be 3, but received {x.ndim}."
+        )
+
     if _non_static_mode():
         if default_main_program().random_seed != 0:
             seed = default_main_program().random_seed