BUG: to_datetime with unit mapping ignores utc and box arguments
- [ ] closes #23760
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @jzhaojieh! Thanks for updating the PR.

 - In the file [`pandas/core/dtypes/concat.py`](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/dtypes/concat.py), following                are the PEP8 issues :
> [Line 215:53](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/dtypes/concat.py#L215): [W291](https://duckduckgo.com/?q=pep8%20W291) trailing whitespace


 - In the file [`pandas/core/tools/datetimes.py`](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py), following                are the PEP8 issues :
> [Line 565:1](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py#L565): [W293](https://duckduckgo.com/?q=pep8%20W293) blank line contains whitespace
> [Line 599:1](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py#L599): [E305](https://duckduckgo.com/?q=pep8%20E305) expected 2 blank lines after class or function definition, found 0
> [Line 599:3](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py#L599): [E227](https://duckduckgo.com/?q=pep8%20E227) missing whitespace around bitwise or shift operator
> [Line 599:7](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py#L599): [E225](https://duckduckgo.com/?q=pep8%20E225) missing whitespace around operator
> [Line 600:3](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py#L600): [E225](https://duckduckgo.com/?q=pep8%20E225) missing whitespace around operator
> [Line 600:5](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py#L600): [E225](https://duckduckgo.com/?q=pep8%20E225) missing whitespace around operator
> [Line 600:7](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py#L600): [E225](https://duckduckgo.com/?q=pep8%20E225) missing whitespace around operator
> [Line 601:5](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py#L601): [E113](https://duckduckgo.com/?q=pep8%20E113) unexpected indentation
> [Line 603:7](https://github.com/jzhaojieh/pandas/blob/638566fc03025323ba91edfef492de38eba484c0/pandas/core/tools/datetimes.py#L603): [E225](https://duckduckgo.com/?q=pep8%20E225) missing whitespace around operator




##### Comment last updated on December 03, 2018 at 22:56 Hours UTC @jzhaojieh can you remove your comments with prints... from the PR please @jzhaojieh it's better to open a pull request when you finish your work. The maintainers of the project usually receive notifications of updates to PR, and the continuous integration, which has usually a long queue, will run tests for every change you push.

Closing this for now, feel free to reopen or create a new PR when you finish. @datapythonista Is there a way for me to run the continuous integration tests without creating a PR? yes, `python -m pytest pandas` should run the tests locally. You should have all the info here: https://pandas.pydata.org/pandas-docs/stable/contributing.html (if something is not clear in that document, feel free to ask me, and then you can clarify it in a PR).