Draft: Decompose template_test.go into individual template test files

Problem to solve

As described in #140 (closed) we're trying to simplify the template tests as the file in question is quite large.

Proposed solution

Decompose template_test.go into individual test files for each template.

Where I could use some help

• Should these new test files be in the same package?
• If we use a shared package, is there a best practice for having shared test helper functions?
• What else did I miss? 😁