Slightly alter Keras dummy loss (#20232)

* Slightly alter Keras dummy loss

* Slightly alter Keras dummy loss

* Add sample weight to test_keras_fit

* Fix test_keras_fit for datasets

* Skip the sample_weight stuff for models where the model tester has no batch_size

tests/test_modeling_tf_common.py

@@ -1544,6 +1544,11 @@ class TFModelTesterMixin:
             else:
                 metrics = []
 
+            if hasattr(self.model_tester, "batch_size"):
+                sample_weight = tf.convert_to_tensor([0.5] * self.model_tester.batch_size, dtype=tf.float32)
+            else:
+                sample_weight = None
+
             model(model.dummy_inputs)  # Build the model so we can get some constant weights
             model_weights = model.get_weights()
 
@@ -1553,6 +1558,7 @@ class TFModelTesterMixin:
             history1 = model.fit(
                 prepared_for_class,
                 validation_data=prepared_for_class,
+                sample_weight=sample_weight,
                 steps_per_epoch=1,
                 validation_steps=1,
                 shuffle=False,
@@ -1588,6 +1594,7 @@ class TFModelTesterMixin:
                 inputs_minus_labels,
                 labels,
                 validation_data=(inputs_minus_labels, labels),
+                sample_weight=sample_weight,
                 steps_per_epoch=1,
                 validation_steps=1,
                 shuffle=False,
@@ -1605,14 +1612,22 @@ class TFModelTesterMixin:
 
             # Make sure fit works with tf.data.Dataset and results are consistent
             dataset = tf.data.Dataset.from_tensor_slices(prepared_for_class)
+
+            if sample_weight is not None:
+                # Add in the sample weight
+                weighted_dataset = dataset.map(lambda x: (x, None, tf.convert_to_tensor(0.5, dtype=tf.float32)))
+            else:
+                weighted_dataset = dataset
             # Pass in all samples as a batch to match other `fit` calls
+            weighted_dataset = weighted_dataset.batch(len(dataset))
             dataset = dataset.batch(len(dataset))
 
             # Reinitialize to fix batchnorm again
             model.set_weights(model_weights)
 
+            # To match the other calls, don't pass sample weights in the validation data
             history3 = model.fit(
-                dataset,
+                weighted_dataset,
                 validation_data=dataset,
                 steps_per_epoch=1,
                 validation_steps=1,