test(config): add unit tests for ParseConfigFile and ReplaceGlobalConfig

- Cover symlink resolution for Kubernetes-style ConfigMap mounts\n- Validate error path for missing file\n- Verify ReplaceGlobalConfig updates global getter\n\nAddresses review comment for config.go:318

Author: tao12345666333

src/semantic-router/pkg/config/parse_configfile_test.go

@@ -0,0 +1,62 @@
+package config_test
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+
+	"github.com/vllm-project/semantic-router/semantic-router/pkg/config"
+)
+
+var _ = Describe("ParseConfigFile and ReplaceGlobalConfig", func() {
+	var tempDir string
+
+	BeforeEach(func() {
+		var err error
+		tempDir, err = os.MkdirTemp("", "config_parse_test")
+		Expect(err).NotTo(HaveOccurred())
+	})
+
+	AfterEach(func() {
+		os.RemoveAll(tempDir)
+		config.ResetConfig()
+	})
+
+	It("should parse configuration via symlink path", func() {
+		if runtime.GOOS == "windows" {
+			Skip("symlink test is skipped on Windows")
+		}
+
+		// Create real config target
+		target := filepath.Join(tempDir, "real-config.yaml")
+		content := []byte("default_model: test-model\n")
+		Expect(os.WriteFile(target, content, 0o644)).To(Succeed())
+
+		// Create symlink pointing to target
+		link := filepath.Join(tempDir, "link-config.yaml")
+		Expect(os.Symlink(target, link)).To(Succeed())
+
+		cfg, err := config.ParseConfigFile(link)
+		Expect(err).NotTo(HaveOccurred())
+		Expect(cfg).NotTo(BeNil())
+		Expect(cfg.DefaultModel).To(Equal("test-model"))
+	})
+
+	It("should return error when file does not exist", func() {
+		_, err := config.ParseConfigFile(filepath.Join(tempDir, "no-such.yaml"))
+		Expect(err).To(HaveOccurred())
+		Expect(err.Error()).To(ContainSubstring("failed to read config file"))
+	})
+
+	It("should replace global config and reflect via GetConfig", func() {
+		// new config instance
+		newCfg := &config.RouterConfig{DefaultModel: "new-default"}
+		config.ReplaceGlobalConfig(newCfg)
+		got := config.GetConfig()
+		Expect(got).To(Equal(newCfg))
+		Expect(got.DefaultModel).To(Equal("new-default"))
+	})
+})