How to load environment variables in Flask unit test

Question

I'm trying to test an app which relies on several environment variables (API keys, mostly). I'd like to keep those as variables instead of putting them directly into a config file, but my unit tests (using unittest) won't run because the environment variables aren't loaded when the test mounts.

I've tried calling load_dotenv in setUp (see below) but that doesn't make a difference. How can I ensure that the test suite reads the environment variables correctly?

.flaskenv

FLASK_APP=myapp.py
BASE_URI='https://example.com'
OTHER_API_KEY='abc123itsasecret'

config.py

import os
basedir = os.path.abspath(os.path.dirname(__file__))

class Config(object):
    SQLALCHEMY_DATABASE_URI = "sqlite:///"
    API_URL = os.environ.get('BASE_URI') + "/api/v1"
    SECRET_KEY = os.environ.get('OTHER_API_KEY')

test_file.py

import os
from dotenv import load_dotenv
import config

basedir = os.path.abspath(os.path.dirname(__file__))

class TestTheThing(unittest.TestCase):
    def setUp(self):
        load_dotenv(os.path.join(basedir, '.flaskenv'))
        app.config.from_object(config.Config)
        app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite://"
        db.create_all()
        self.client = app.test_client()

In the console after running python -m unittest myapp.test_file

File "/../../package/config.py", line 29, in Config
    'API_URL': os.environ.get('BASE_URI') + 'api/v1/',
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

Answer 1

After reading more, I realized that I needed to load the variables in my config file, not in the test runner. Adding load_dotenv to the top of the config file allowed tests to run.

config.py

import os
from dotenv import load_dotenv

basedir = os.path.abspath(os.path.dirname(__file__))

load_dotenv(os.path.join(basedir, '.flaskenv'))
# rest of file

I spent time trying to figure out where the crash was happening. I added a breakpoint inside setUp that never got hit, so it had to be earlier in the execution.

Reading the stack trace more carefully, it was caused by importing app at the top of the test file. When the app is imported, it tries to pull all the variables in before it could call load_dotenv inside setUp. Loading environment variables before the config object was loaded into the Flask object cleared it up.