Implement-LLM-WP-0005-cost-model-estimators

tests/test_costs.py

@@ -0,0 +1,49 @@
+import pytest
+
+from llm_connect.costs import CostEstimate, CostModel, estimate_cost
+from llm_connect.rates import ModelRate, ModelRateRegistry
+
+
+def test_known_model_cost_matches_lefevre_smoke_budget():
+    estimate = estimate_cost("openai/gpt-4o-mini", 28_000, 7_500)
+
+    assert estimate.cost_source == "rate_table:openai/gpt-4o-mini"
+    assert estimate.cost_usd == pytest.approx(0.0087)
+    assert estimate.cost_usd == pytest.approx(0.009, rel=0.2)
+
+
+def test_unknown_model_returns_unknown_without_zeroing_cost():
+    estimate = estimate_cost("unknown/model", 100, 50)
+
+    assert estimate == CostEstimate(cost_usd=None, cost_source="unknown")
+
+
+def test_registry_override_controls_estimate():
+    registry = ModelRateRegistry(
+        {
+            "vendor/model": ModelRate(
+                "vendor/model",
+                prompt_per_1k=1.0,
+                completion_per_1k=2.0,
+            )
+        }
+    )
+
+    estimate = estimate_cost("vendor/model", 1_000, 500, registry=registry)
+
+    assert estimate.cost_usd == pytest.approx(2.0)
+    assert estimate.prompt_cost_usd == pytest.approx(1.0)
+    assert estimate.completion_cost_usd == pytest.approx(1.0)
+
+
+def test_zero_tokens_are_valid_and_cost_zero_for_known_model():
+    estimate = CostModel().estimate_cost("openai/gpt-4o-mini", 0, 0)
+
+    assert estimate.cost_usd == 0
+    assert estimate.prompt_cost_usd == 0
+    assert estimate.completion_cost_usd == 0
+
+
+def test_negative_tokens_are_rejected():
+    with pytest.raises(ValueError, match="prompt_tokens"):
+        estimate_cost("openai/gpt-4o-mini", -1, 0)