refactor: removed get_test_accessor and renamed vars with meaningfu…

…l txt (#284)

# Rationale for this change

This is a follow up to #261 that further tidies up the related tests.

# What changes are included in this PR?

- Removed the `get_test_accessor` function, replacing it with a
schema-specific accessor.
- Renamed variables like `i`, `i0`, `i1`, and `s` to more meaningful
names like `salary`, `department`, `tax`, and `name` reflecting the
context of the data.


# Are these changes tested?
These changes are in tests.