test: add (failing) test coverage for field validators

projects/fal/tests/test_pydantic.py

@@ -4,7 +4,7 @@
 
 import dill
 import dill._dill as dill_serialization
-from pydantic import BaseModel, Field, model_validator
+from pydantic import BaseModel, Field, field_validator, model_validator
 
 
 def build_pydantic_model(
@@ -77,8 +77,9 @@ class Input(BaseModel):
                             validators (for the purpose of testing).
     """
 
-    prompt: str = Field()
+    prompt: str = ...
     num_steps: int = Field(default=2, ge=1, le=10)
+    epochs: int = 10
     validation_counter: int = 0
 
     def steps_x2(self) -> int:
@@ -87,9 +88,15 @@ def steps_x2(self) -> int:
         Computes double of the `num_steps` field value."""
         return self.num_steps * 2
 
+    @field_validator("epochs")
+    @classmethod
+    def triple_epochs(cls, v: int) -> int:
+        """A field validator that multiplies the validated field value by 10."""
+        return v * 3
+
     @model_validator(mode="after")
-    def validate_num_steps(self) -> None:
-        """A model post-validator."""
+    def increment(self) -> None:
+        """A model post-validator that increments a counter."""
         self.validation_counter += 100
 
 
@@ -108,9 +115,9 @@ def deserialise_pydantic_model():
     """
     dill.settings["recurse"] = True
     serialized_cls = dill.dumps(Input)
-    print("====== DESERIALIZING =====")
+    print("===== DESERIALIZING =====")
     model_cls = dill.loads(serialized_cls)
-    print("======== RUNNING =====")
+    print("===== INSTANTIATING =====")
     model = model_cls(prompt="a")
     return model
 
@@ -122,7 +129,8 @@ def validate_deserialisation(model: Input) -> None:
     assert prompt == "a", f"Prompt not retrieved: expected 'a' got {prompt!r}"
     assert steps == 2, f"Steps not retrieved: expected 2 got {steps!r}"
     assert steps_x2 == 4, f"Incorrect `steps_x2()`: expected 4 got {steps_x2}"
-    assert model.validation_counter == 100
+    assert model.epochs == 30, "The `validate_epochs` field validator didn't run"
+    assert model.validation_counter == 100, "The `increment` model validator didn't run"
     return