Add AV1602: Postfix test classes with Specs instead of Tests

_rules/1602.md

@@ -0,0 +1,23 @@
+---
+rule_id: 1602
+rule_category: testability
+title: Postfix test classes with `Specs` instead of `Tests`
+severity: 3
+---
+The suffix `Specs` signals that a class describes the observable behavior (specifications) of a component, not just a set of mechanical tests. This encourages a behavior-driven mindset.
+
+```csharp
+// Avoid
+public class OrderServiceTests { ... }
+
+// Prefer
+public class OrderServiceSpecs { ... }
+
+// Or nest specs per scenario
+public class OrderServiceSpecs
+{
+    public class Order_placement { ... }
+}
+```
+
+Nested classes group related scenarios together and make the test report more readable.