test: add unit tests for config loader

internal/config/config_test.go

@@ -0,0 +1,44 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadConfig_NotFound(t *testing.T) {
+	_, err := Load("non_existent_config_file_12345.json")
+	if err == nil {
+		t.Fatal("expected error when loading non-existent config, got nil")
+	}
+}
+
+func TestLoadConfig_ValidJSON(t *testing.T) {
+	tmpDir := t.TempDir()
+	tmpFile := filepath.Join(tmpDir, "config.json")
+
+	content := []byte(`{
+		"telegram_token": "test_token",
+		"gemini_api_key": "test_key",
+		"gemini_base_url": "http://localhost:8080"
+	}`)
+
+	if err := os.WriteFile(tmpFile, content, 0644); err != nil {
+		t.Fatalf("failed to write temp config file: %v", err)
+	}
+
+	cfg, err := Load(tmpFile)
+	if err != nil {
+		t.Fatalf("failed to load valid config: %v", err)
+	}
+
+	if cfg.TelegramToken != "test_token" {
+		t.Errorf("expected telegram_token 'test_token', got '%s'", cfg.TelegramToken)
+	}
+	if cfg.GeminiApiKey != "test_key" {
+		t.Errorf("expected gemini_api_key 'test_key', got '%s'", cfg.GeminiApiKey)
+	}
+	if cfg.GeminiBaseURL != "http://localhost:8080" {
+		t.Errorf("expected gemini_base_url 'http://localhost:8080', got '%s'", cfg.GeminiBaseURL)
+	}
+}