test to validate merge of derived buffer

tests/test_desire_merge.py

@@ -1,5 +1,5 @@
 from service_capacity_modeling.capacity_planner import planner
-from service_capacity_modeling.interface import Buffer
+from service_capacity_modeling.interface import Buffer, BufferIntent
 from service_capacity_modeling.interface import BufferComponent
 from service_capacity_modeling.interface import Buffers
 from service_capacity_modeling.interface import CapacityDesires
@@ -25,6 +25,9 @@
         desired={
             "custom": Buffer(ratio=3.8, components=["custom"]),
             "custom-cpu": Buffer(ratio=3.0, components=[BufferComponent.cpu]),
+        },
+        derived={
+            "compute": Buffer(intent=BufferIntent.scale, ratio=2, components=["compute"])
         }
     ),
 )
@@ -41,6 +44,9 @@ def test_cassandra_merge():
     assert merged.query_pattern.estimated_read_per_second.mid == 100000
     assert merged.query_pattern.estimated_mean_read_size_bytes.low == 10
     assert merged.data_shape.estimated_state_size_gib.mid == 10
+    assert merged.buffers.derived.get("compute") is not None
+    assert merged.buffers.derived["compute"].ratio == 2.0
+    assert merged.buffers.derived["compute"].intent == BufferIntent.scale
 
     # Should come from cassandra model
     assert merged.query_pattern.estimated_mean_read_latency_ms.mid == 2.0