Add comprehensive tests for Parks API and models

- Implemented extensive test cases for the Parks API, covering endpoints for listing, retrieving, creating, updating, and deleting parks.
- Added tests for filtering, searching, and ordering parks in the API.
- Created tests for error handling in the API, including malformed JSON and unsupported methods.
- Developed model tests for Park, ParkArea, Company, and ParkReview models, ensuring validation and constraints are enforced.
- Introduced utility mixins for API and model testing to streamline assertions and enhance test readability.
- Included integration tests to validate complete workflows involving park creation, retrieval, updating, and deletion.

parks/models/parks.py

@@ -17,6 +17,11 @@ if TYPE_CHECKING:
 
 @pghistory.track()
 class Park(TrackedModel):
+    
+    # Import managers
+    from ..managers import ParkManager
+    
+    objects = ParkManager()
     id: int  # Type hint for Django's automatic id field
     STATUS_CHOICES = [
         ("OPERATING", "Operating"),
@@ -81,6 +86,43 @@ class Park(TrackedModel):
 
     class Meta:
         ordering = ["name"]
+        constraints = [
+            # Business rule: Closing date must be after opening date
+            models.CheckConstraint(
+                name="park_closing_after_opening",
+                check=models.Q(closing_date__isnull=True) | models.Q(opening_date__isnull=True) | models.Q(closing_date__gte=models.F("opening_date")),
+                violation_error_message="Closing date must be after opening date"
+            ),
+            # Business rule: Size must be positive
+            models.CheckConstraint(
+                name="park_size_positive",
+                check=models.Q(size_acres__isnull=True) | models.Q(size_acres__gt=0),
+                violation_error_message="Park size must be positive"
+            ),
+            # Business rule: Rating must be between 1 and 10
+            models.CheckConstraint(
+                name="park_rating_range",
+                check=models.Q(average_rating__isnull=True) | (models.Q(average_rating__gte=1) & models.Q(average_rating__lte=10)),
+                violation_error_message="Average rating must be between 1 and 10"
+            ),
+            # Business rule: Counts must be non-negative
+            models.CheckConstraint(
+                name="park_ride_count_non_negative",
+                check=models.Q(ride_count__isnull=True) | models.Q(ride_count__gte=0),
+                violation_error_message="Ride count must be non-negative"
+            ),
+            models.CheckConstraint(
+                name="park_coaster_count_non_negative",
+                check=models.Q(coaster_count__isnull=True) | models.Q(coaster_count__gte=0),
+                violation_error_message="Coaster count must be non-negative"
+            ),
+            # Business rule: Coaster count cannot exceed ride count
+            models.CheckConstraint(
+                name="park_coaster_count_lte_ride_count",
+                check=models.Q(coaster_count__isnull=True) | models.Q(ride_count__isnull=True) | models.Q(coaster_count__lte=models.F("ride_count")),
+                violation_error_message="Coaster count cannot exceed total ride count"
+            ),
+        ]
 
     def __str__(self) -> str:
         return self.name