optimize: 使用 is_file 代替字符串结尾判断

[netlify[bot]]

✅ Deploy Preview for pay-yansongda canceled.

Name	Link
🔨 Latest commit	a8011650ca8adc177d3be0422d84ecc714039f19
🔍 Latest deploy log	https://app.netlify.com/sites/pay-yansongda/deploys/664609717e64cd0008a03c2b

[yansongda]

帮忙加下单元测试

[NotMings]

帮忙加下单元测试

不需要单元测试吧。并没有添加新的功能

[yansongda]

OK，看到了

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.50%. Comparing base (747806e) to head (a801165).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #982 +/- ## ========================================= Coverage 97.50% 97.50% Complexity 907 907 ========================================= Files 347 347 Lines 6201 6201 ========================================= Hits 6046 6046 Misses 155 155 ```

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