[devin-ai-integration]

Summary

get_effective_cost had no test asserting its output: the mocked cost tests hard-code cached_tokens = 0 and only assert token totals, so the cache-read/cache-write arithmetic was multiplied by zero in every non-pricy test. This adds unit tests that assert exact effective-cost floats for both providers with non-zero cache tokens, and fixes the bug the tests immediately exposed.

Bug: the Anthropic branch read cache-read tokens from a field the Anthropic API does not emit, so all cache-read cost was silently dropped:

-cache_read_tokens = getattr(usage, "cache_input_tokens", 0)
+cache_read_tokens = getattr(usage, "cache_read_input_tokens", None)
+if cache_read_tokens is None:
+    cache_read_tokens = getattr(usage, "cache_input_tokens", 0)

The old name is kept as a fallback so any caller/response still using it keeps working.

New tests in tests/llm/test_tracking.py drive a tiny _CostModel(TrackAPIPricingMixin) with fixed input_cost/output_cost (no provider, no pricing fetch) and cover:

• Anthropic with non-zero cache_read_input_tokens + cache_creation_input_tokens, and without cache tokens
• OpenAI chat-completion branch (prompt_tokens_details) with cached tokens and with prompt_tokens_details = None
• OpenAI responses branch (input_tokens_details) with cached tokens
• usage is None → 0.0, unsupported provider → 0.0, litellm → completion_cost
• __call__ accumulating stats["effective_cost"] across two calls

Plain MagicMock cannot be used for the OpenAI dispatch (hasattr(usage, "prompt_tokens_details") is always true on a mock), hence the small _FakeUsage helper, which also supports dict(usage) as TrackAPIPricingMixin.__call__ requires.

Devin-Org: engineering

Link to Devin session: https://app.devin.ai/sessions/25cba9f25dfd4bd6985865c065a92a08
Open in Devin Desktop: https://app.devin.ai/desktop/session/25cba9f25dfd4bd6985865c065a92a08?variant=devin

[devin-ai-integration]

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