test: split endpoint resolver tests (#4957)

tests/test_endpoint_resolver_headers.py

@@ -0,0 +1,16 @@
+"""Tests for endpoint_resolver — request header construction."""
+from src.endpoint_resolver import build_headers
+
+
+class TestBuildHeaders:
+    def test_no_key(self):
+        assert build_headers(None, "https://api.openai.com/v1") == {}
+
+    def test_openai_bearer(self):
+        assert build_headers("sk-abc", "https://api.openai.com/v1") == {"Authorization": "Bearer sk-abc"}
+
+    def test_anthropic_headers(self):
+        assert build_headers("sk-ant-abc", "https://api.anthropic.com") == {"x-api-key": "sk-ant-abc", "anthropic-version": "2023-06-01"}
+
+    def test_empty_key(self):
+        assert build_headers("", "https://api.openai.com/v1") == {}