Refactor testing set up

[YaleChen299]

In #80, the set-up relies on relative paths for the env file and the migration files. This may make it less maintainable in the future. To be refactored to remove this dependency on relative paths.

Moreover, the destination for the env file and migration files needs to be reiterated everywhere it is used, which is undesirable.

[RichDom2185]

Furthermore, there is quite a bit of code duplication between the DB scripts and test framework. We will need to investigate how this is usually done in other Golang codebases out there.