equality and hash operators [equality_on_batches]

Author: hjwp

model.py

@@ -19,6 +19,14 @@ def __init__(self, ref: str, sku: str, qty: int, eta: Optional[date]):
         self._purchased_quantity = qty
         self._allocations = set()  # type: Set[OrderLine]
 
+    def __eq__(self, other):
+        if not isinstance(other, Batch):
+            return False
+        return other.reference == self.reference
+
+    def __hash__(self):
+        return hash(self.reference)
+
     def allocate(self, line: OrderLine):
         if self.can_allocate(line):
             self._allocations.add(line)