What exactly are Harnesses and Fixtures in the Ruby?

Fixtures and test harnesses are important concepts in Ruby on Rails testing:

Fixtures are sample data that you can use to populate your testing database before running tests. They are stored in YAML files, one file per model, in the test/fixtures directory[1][3]. Fixtures allow you to create predefined data to use in your tests, rather than having to create it manually each time[4].

For example, a fixture for an Article model might look like this[3]:

first:
  title: Welcome to Rails!
  category: about

This creates a fixture named first with a title and category attribute.

Test harnesses provide automation to run your tests. Rails includes a built-in test harness that allows you to run unit tests to verify individual components like models and controllers work correctly[5]. The test harness will automatically load fixtures into the test database before running tests[1]....