[GenerationOutputs] Fix GenerationOutputs Tests (#9443)

* fix generation models

* fix led

* fix docs

* add is_decoder

* fix last docstrings

* make style

* fix t5 cross attentions

* correct t5

tests/test_modeling_led.py

@@ -327,6 +327,32 @@ class LEDModelTest(ModelTesterMixin, GenerationTesterMixin, unittest.TestCase):
         # longformer cannot keep gradients in attentions or hidden states
         return
 
+    def _check_encoder_attention_for_generate(self, attentions, batch_size, config, seq_length):
+        # make sure tgt_length is padded
+        tgt_length = (
+            seq_length // config.attention_window[0] + (seq_length % config.attention_window[0] != 0)
+        ) * config.attention_window[0]
+
+        encoder_expected_shape = (batch_size, config.num_attention_heads, tgt_length, seq_length)
+        self.assertIsInstance(attentions, tuple)
+        self.assertListEqual(
+            [layer_attentions.shape for layer_attentions in attentions],
+            [encoder_expected_shape] * len(attentions),
+        )
+
+    def _check_encoder_hidden_states_for_generate(self, hidden_states, batch_size, config, seq_length):
+        # make sure seq_length is padded
+        seq_length = (
+            seq_length // config.attention_window[0] + (seq_length % config.attention_window[0] != 0)
+        ) * config.attention_window[0]
+
+        encoder_expected_shape = (batch_size, seq_length, config.hidden_size)
+        self.assertIsInstance(hidden_states, tuple)
+        self.assertListEqual(
+            [layer_hidden_states.shape for layer_hidden_states in hidden_states],
+            [encoder_expected_shape] * len(hidden_states),
+        )
+
     def test_attention_outputs(self):
         config, inputs_dict = self.model_tester.prepare_config_and_inputs_for_common()
         config.return_dict = True