如果将db连接存储在flask.g对象上，如何使Flask连接到测试数据库？

Question

I have a Flask application using pymysql directly, no SQLAlchemy.

In my db.py file, I have the following:

from myns.my_db import db_connect

def has_db():
  return hasattr(flask.g, 'db')

def get_db(name):
  if not has_db():
    setattr(flask.g, 'db', db_connect())
  return getattr(flask.g, 'db')

As well as this in my main app.py:

@app.teardown_request
def close_db(ex):
  if has_db():
    conn = get_db()
    conn.close()

What I'm trying to do is "mock" the database in tests, using the example here: https://flask.palletsprojects.com/en/1.1.x/testing/#faking-resources-and-context

The error I'm getting when running my test is:

pymysql.err.InterfaceError: (0, '')

Which I have encountered before with pymysql. I generally interpret this error to mean that there are multiple threads using a database cursor, or there is a global database cursor being used inside multiple modules. This seems to make sense, because I believe the flask.g object to be some kind of thred-local global object.

Is there a way to "mock" the database connection in my test, even if it involves re-architecting my Flask application? Thanks!

Answer 1

The problem was that I had a self.db connection that I was trying to use to:

1. Setup the database and install the schema
2. Run the tests against
3. And also teardown the database

Once I separated those steps and used a new connection for steps 1, 2 and 3, I no longer had the issue.