test(llmobs): cover google-genai metrics and streaming output formatting

The `extractMetrics` token fallback (derive the total from prompt +
candidate counts when `totalTokenCount` is absent) and the streaming
special-case branch in `formatOutputMessages` (functionCall /
executableCode / codeExecutionResult parts routed through non-streaming
formatting) had no direct coverage. Add a unit spec pinning both
branches and their token-count siblings.

Author: BridgeAR

packages/dd-trace/test/llmobs/plugins/google-genai/util.spec.js

@@ -0,0 +1,65 @@
+'use strict'
+
+const assert = require('node:assert')
+const { describe, it } = require('mocha')
+
+const { extractMetrics, formatOutputMessages } = require('../../../../src/llmobs/plugins/genai/util')
+
+describe('google-genai llmobs util', () => {
+  describe('extractMetrics', () => {
+    it('derives totalTokens from prompt and candidate counts when totalTokenCount is absent', () => {
+      const metrics = extractMetrics({ usageMetadata: { promptTokenCount: 5, candidatesTokenCount: 7 } })
+      assert.deepStrictEqual(metrics, { inputTokens: 5, outputTokens: 7, totalTokens: 12 })
+    })
+
+    it('prefers totalTokenCount over the derived sum when present', () => {
+      const metrics = extractMetrics({
+        usageMetadata: { promptTokenCount: 5, candidatesTokenCount: 7, totalTokenCount: 20 },
+      })
+      assert.deepStrictEqual(metrics, { inputTokens: 5, outputTokens: 7, totalTokens: 20 })
+    })
+
+    it('omits totalTokens when no token counts are present', () => {
+      assert.deepStrictEqual(extractMetrics({ usageMetadata: {} }), {})
+    })
+
+    it('returns no metrics when usageMetadata is missing', () => {
+      assert.deepStrictEqual(extractMetrics({}), {})
+    })
+  })
+
+  describe('formatOutputMessages with streaming special cases', () => {
+    function streamingResponse (part) {
+      return { candidates: [{ content: { parts: [part] } }] }
+    }
+
+    it('routes a streaming functionCall part through non-streaming formatting', () => {
+      const part = { functionCall: { name: 'getWeather', args: { city: 'NYC' }, id: 'call_1' } }
+      assert.deepStrictEqual(formatOutputMessages(streamingResponse(part), true), [{
+        role: 'assistant',
+        toolCalls: [{ name: 'getWeather', arguments: { city: 'NYC' }, toolId: 'call_1', type: 'function_call' }],
+      }])
+    })
+
+    it('routes a streaming executableCode part through non-streaming formatting', () => {
+      const part = { executableCode: { language: 'PYTHON', code: 'print(1)' } }
+      assert.deepStrictEqual(formatOutputMessages(streamingResponse(part), true), [{
+        role: 'assistant',
+        content: JSON.stringify({ language: 'PYTHON', code: 'print(1)' }),
+      }])
+    })
+
+    it('routes a streaming codeExecutionResult part through non-streaming formatting', () => {
+      const part = { codeExecutionResult: { outcome: 'OUTCOME_OK', output: '1\n' } }
+      assert.deepStrictEqual(formatOutputMessages(streamingResponse(part), true), [{
+        role: 'assistant',
+        content: JSON.stringify({ outcome: 'OUTCOME_OK', output: '1\n' }),
+      }])
+    })
+
+    it('accumulates plain text streaming parts by role', () => {
+      const response = { candidates: [{ content: { parts: [{ text: 'Hello, ' }, { text: 'world!' }] } }] }
+      assert.deepStrictEqual(formatOutputMessages(response, true), [{ role: 'assistant', content: 'Hello, world!' }])
+    })
+  })
+})