Add AV1610: Use Test Data Builders or Object Mothers to construct test objects

_rules/1610.md

@@ -0,0 +1,25 @@
+---
+rule_id: 1610
+rule_category: testability
+title: Use Test Data Builders or Object Mothers to construct test objects
+severity: 2
+---
+When setting up test data, avoid scattering `new SomeObject(...)` constructors across many tests. This makes tests hard to maintain when the object's constructor changes, and makes it hard to understand which properties matter to the test.
+
+Use a **Test Data Builder** when you need flexible control over many properties:
+
+```csharp
+var order = new OrderBuilder()
+    .WithCustomer(customer)
+    .WithStatus(OrderStatus.Pending)
+    .Build();
+```
+
+Use an **Object Mother** (a simple static factory method) when you have a small number of canonical test objects that are reused as-is:
+
+```csharp
+var order = TestOrders.PendingOrder();
+var order = TestOrders.ShippedOrder();
+```
+
+Both approaches make tests more readable and resilient to object construction changes. Prefer builders when flexibility is needed, and object mothers when a few fixed examples are sufficient.