Use "with execute as 'dbo' "

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-- Prep

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-- Create test users and test db

USE [master]

GO

CREATE LOGIN [testAdmin] WITH PASSWORD=N'Dork', DEFAULT_DATABASE=[master], CHECK_EXPIRATION=OFF, CHECK_POLICY=OFF

GO

CREATE LOGIN [testUser] WITH PASSWORD=N'Dork', DEFAULT_DATABASE=[master], CHECK_EXPIRATION=OFF, CHECK_POLICY=OFF

GO

CREATE DATABASE [testDB]...