Documentation improvement for backend testing.

[thedroiddiv]

Checklist

• [x] You have not changed whitespace unnecessarily (it makes diffs hard to read)
• [x] You have a descriptive commit message with a short title (first line, max 50 chars).
• [x] Your code follows the style of the project (e.g. never omit braces in if statements)
• [ ] You have commented your code, particularly in hard-to-understand areas
• [x] You have performed a self-review of your own code
• [ ] UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• [ ] UI Changes: You have tested your change using the Google Accessibility Scanner