Update integration tests paragraph in testing chapter

[sarahcollyer]

Issue Template

Title: Update integration tests paragraph in testing chapter
Author: Sarah Collyer

Issue or Suggestion

The current paragraph for integration tests should be updated to reflect similar language as used in the end-to-end tests section below it. This should be written using plain English.

Proposed Change

New wording to introduce integration tests.

Type of Change Requested

[x] Fixing Existing Content
[ ] Add Additional Content to Existing Page
[ ] New Content

Additional Context / Screenshots

Add any other context or screenshots about the suggestion here