Avoid flaky generation sampling tests (#21445)

* fix

* fix

---------
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

tests/generation/test_utils.py

@@ -780,7 +780,7 @@ class GenerationTesterMixin:
                 forced_eos_token_id=model.config.forced_eos_token_id,
                 max_length=max_length,
             )
-            logits_warper_kwargs, logits_warper = self._get_warper_and_kwargs(num_beams=1)
+            logits_warper_kwargs, logits_warper = self._get_warper_and_kwargs(num_beams=2)
 
             # check `generate()` and `sample()` are equal
             output_sample, output_generate = self._sample_generate(

tests/models/switch_transformers/test_modeling_switch_transformers.py

@@ -621,7 +621,7 @@ class SwitchTransformersModelTest(ModelTesterMixin, GenerationTesterMixin, unitt
             config.forced_eos_token_id = None
 
             model = model_class.from_pretrained("google/switch-base-8").to(torch_device).eval()
-            logits_warper_kwargs, logits_warper = self._get_warper_and_kwargs(num_beams=1)
+            logits_warper_kwargs, logits_warper = self._get_warper_and_kwargs(num_beams=2)
 
             num_return_sequences = 2
             if model.config.is_encoder_decoder:
@@ -670,7 +670,7 @@ class SwitchTransformersModelTest(ModelTesterMixin, GenerationTesterMixin, unitt
             config.eos_token_id = None
             config.forced_eos_token_id = None
 
-            logits_warper_kwargs, logits_warper = self._get_warper_and_kwargs(num_beams=1)
+            logits_warper_kwargs, logits_warper = self._get_warper_and_kwargs(num_beams=2)
 
             model = model_class.from_pretrained("google/switch-base-8").to(torch_device).eval()