Look at adding helpers for integration tests

As of recent versions of Rails, they've begun discouraging the use of `ActionController::TestCase` for new tests and encouraging the use of integration tests based around `ActionDispatch::IntegrationTest`. The helpers in this gem are still based around the previous style; we may need to look at implementing a second set of helpers to enable the use of integration tests.

See: https://api.rubyonrails.org/classes/ActionController/TestCase.html

Start by reading the linked ActionController::TestCase documentation and comparing it with ActionDispatch::IntegrationTest. Then inspect the gem's existing test helpers to determine what a second integration-test-oriented helper set would need to support; done means the required scope and behavior are defined and implemented with coverage for integration tests.

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