Support database interaction in tests

We want our integration tests to run against a test database.  This
allows us to create more specific tests (e.g. predict ID values) in
addition to making sure we don't interact with real data.

I decided to use the PostgreSQL schema support instead of requiring
a separate `TEST_DATABASE_URL`.  This means there is less setup for
a dev environment but also makes it easier for us to drop / create the
schema as part of the tests.

.gitlab-ci.yml

@@ -27,8 +27,13 @@ test:
     S3_ENDPOINT: "https://example.com"
     S3_REGION: "us-east-1"
     S3_BUCKET: "example"
-    DATABASE_URL: "postgresql://test_user:password@localhost/test_database"
+    # Used by gitlab CI to create the database
     POSTGRES_DB: "test_database"
     POSTGRES_USER: "test_user"
     POSTGRES_PASSWORD: "password"
     POSTGRES_HOST_AUTH_METHOD: trust
+    # Used by our code to connect to the database
+    PGHOST: 'localhost'
+    PGDATABASE: 'test_database'
+    PGUSER: 'test_user'
+    PGPASSWORD: 'password'

Makefile

@@ -16,7 +16,7 @@ install:
 	pip install -r requirements-dev.txt
 
 test:
-	pytest tests/
+	APP_SCHEMA=test pytest tests/
 
 migrate:
 	alembic upgrade head

tests/conftest.py

+import pytest
+from sqlalchemy import text
+
+from alembic import command
+from alembic.config import Config
+from service.core.database import engine
+from service.core.settings import settings
+
+
+def assert_app_schema_is_not_public():
+    if settings.APP_SCHEMA == "public":
+        pytest.exit(
+            "You must override APP_SCHEMA to a value other than `public` when running tests. These tests are data-destructive."
+        )
+
+
+def drop_and_create_configured_schema():
+    assert_app_schema_is_not_public()  # This is intentionally / defensively redundant since we're about to drop the schema.
+    with engine.connect() as connection:
+        connection.execute(text(f"DROP SCHEMA IF EXISTS {settings.APP_SCHEMA} CASCADE"))
+        connection.execute(text(f"CREATE SCHEMA IF NOT EXISTS {settings.APP_SCHEMA}"))
+        connection.commit()
+
+
+def drop_configured_schema():
+    with engine.connect() as connection:
+        connection.execute(text(f"DROP SCHEMA IF EXISTS {settings.APP_SCHEMA} CASCADE"))
+        connection.commit()
+
+
+def run_migrations():
+    alembic_cfg = Config("alembic.ini")
+    command.upgrade(alembic_cfg, "head")
+
+
+@pytest.hookimpl(tryfirst=True)
+def pytest_sessionstart():
+    assert_app_schema_is_not_public()
+
+
+@pytest.fixture(scope="function", autouse=True)
+def setup_and_teardown_db():
+    drop_and_create_configured_schema()
+    run_migrations()
+
+    yield
+
+    drop_configured_schema()