refactor: 封装 Redis key 生成函数

backend/internal/repository/api_key_cache_test.go

@@ -0,0 +1,46 @@
+//go:build unit
+
+package repository
+
+import (
+	"math"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestApiKeyRateLimitKey(t *testing.T) {
+	tests := []struct {
+		name     string
+		userID   int64
+		expected string
+	}{
+		{
+			name:     "normal_user_id",
+			userID:   123,
+			expected: "apikey:ratelimit:123",
+		},
+		{
+			name:     "zero_user_id",
+			userID:   0,
+			expected: "apikey:ratelimit:0",
+		},
+		{
+			name:     "negative_user_id",
+			userID:   -1,
+			expected: "apikey:ratelimit:-1",
+		},
+		{
+			name:     "max_int64",
+			userID:   math.MaxInt64,
+			expected: "apikey:ratelimit:9223372036854775807",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := apiKeyRateLimitKey(tc.userID)
+			require.Equal(t, tc.expected, got)
+		})
+	}
+}