Implement test fixtures

[abrichr]

Feature request

We would like to add a file at assets/fixtures.sql that seeds the database with some minimal recording data for running tests.

This task involves:

• creating the sql file (either export a manually created recording, or generate one programmatically)
• adding a conftest.py that creates a new database and seeds it with fixtures before tests run, and tears it down after tests complete (whether or not they pass)

Motivation

Some tests fail if no recording is present