mirror of
https://github.com/jbranchaud/til
synced 2026-08-31 16:51:46 +00:00
62 lines
2.1 KiB
Markdown
62 lines
2.1 KiB
Markdown
# Override Timezone That All Tests Run In
|
||
|
||
I was building out the initial functionality of a Python project in my local dev
|
||
env. I was writing tests along the way to guard against regressions. Many of the
|
||
tests assert things about time, durations, and formatted timestamps. All was
|
||
well.
|
||
|
||
Then I was getting the project setup on GitHub with a CI workflow to run the
|
||
test suite. And a ton of tests were failing. It was all the tests dealing with
|
||
time. They were all off by 5 hours.
|
||
|
||
I recognized that time difference immediately. That's the difference between my
|
||
time here in Chicago and UTC. When I run the tests locally, they are all
|
||
formatted the timezone setting on my machine -- `America/Chicago`. Whereas when
|
||
I run them in this CI environment, they were suddenly being formatted to `UTC`.
|
||
|
||
What I needed to do was explicitly set the timezone that all the tests would
|
||
always run in, regardless of environment.
|
||
|
||
I added the following to my `conftest.py` file:
|
||
|
||
```python
|
||
import os
|
||
import time
|
||
|
||
|
||
# Set the timezone that all tests run in
|
||
os.environ["TZ"] = "America/Chicago"
|
||
time.tzset()
|
||
```
|
||
|
||
First, I set the timezone (`TZ`) in `os.environ` to `America/Chicago`. That's a
|
||
copy of the executing environment that Python makes when it starts up.
|
||
|
||
Second, because `TZ` may be tied to some cached info under the hood, I have to
|
||
also run `time.tzset()`.
|
||
|
||
> Initialize, or reinitialize, the local timezone to the value stored in
|
||
> os.environ[‘TZ’]. The TZ environment variable should be specified in standard
|
||
> Unix timezone format as documented in the tzset man page (eg. ‘US/Eastern’,
|
||
> ‘Europe/Amsterdam’).
|
||
|
||
Now, all of my tests run reliably in `America/Chicago`.
|
||
|
||
To demonstrate all of this from the Python repl, here is an example:
|
||
|
||
```python
|
||
>>> from datetime import datetime
|
||
>>> import os
|
||
>>> import time
|
||
>>> os.environ["TZ"] = "America/Los_Angeles"
|
||
>>> time.tzset()
|
||
>>> datetime.now()
|
||
datetime.datetime(2026, 8, 15, 14, 3, 19, 373682)
|
||
>>> os.environ["TZ"] = "America/Chicago"
|
||
>>> time.tzset()
|
||
>>> datetime.now()
|
||
datetime.datetime(2026, 8, 15, 16, 3, 33, 322803)
|
||
```
|
||
|
||
Notice the two hour difference between those two.
|