bug fix and add tests

Author: FilippoOlivo

pina/_src/condition/condition_base.py

@@ -142,7 +142,7 @@ def switch_dataloader_fn(self, create_dataloader_fn):
         :return: The decorated function with the new dataloader function.
         :rtype: function
         """
-        # Replace the create_dataloader method of the ConditionBase class with 
+        # Replace the create_dataloader method of the ConditionBase class with
         # the new function
         self.has_custom_dataloader_fn = True
         self.create_dataloader = create_dataloader_fn

pina/_src/core/trainer.py

@@ -140,7 +140,11 @@ def __init__(
             )
             batching_mode = "common_batch_size"
 
-        if batch_size == 1 and batching_mode == "proportional":
+        if (
+            batch_size is not None
+            and batch_size <= len(solver.problem.conditions)
+            and batching_mode == "proportional"
+        ):
             warnings.warn(
                 "Batching mode is set to proportional but batch_size is 1. "
                 "Batching mode will be set to common_batch_size.",