[Testing] Establish a pattern for how to use TestMain

[Olshansk]

Objective

Establishing a convention for how to use, name and define TestMain in each individual module

Origin Document

#683 (comment)

Goals

• Creating a standard for file and function naming for test helpers to have consistency and reduce cognitive load
• Make it easier for new developers to follow module specific patterns

Deliverable

• Establishing and documenting a convention for naming test files containing TestMain and helpers in each module
• Updating and renaming all files containing a TestMain function

Non-goals / Non-deliverables

• Modifying the logic existing tests
• Consolidating test helpers across modules (optional)

General issue deliverables

• Update the appropriate CHANGELOG(s)
• Update any relevant local/global README(s)
• Update relevant source code tree explanations

Testing Methodology

• All tests: make test_all

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Creator: @Olshansk
Co-Owners: @bryanchriswhite