Explanation
A test plan is a document that describes the scope, objectives, strategy, and activities of testing a software product or system. A test plan is mandatory in most software development projects because it ensures that the software meets the quality standards and requirements of the stakeholders. A test plan also helps to identify and mitigate the risks, defects, and issues that may affect the software functionality, performance, usability, and security. A test plan is different from a communication management plan, which is a document that describes how the project information will be communicated to the stakeholders. A test plan is also different from a disaster recovery plan, which is a document that describes how the project will resume its operations in the event of a disaster or emergency. A test plan is not a procurement plan, which is a document that describes how the project will acquire the goods and services needed from external sources. References:
CBAP / CCBA Certified Business Analysis Study Guide, 2nd Edition, Chapter 9: Solution Assessment and Validation, page 329-330.
How to write a software requirement document (with template), paragraph 6 These testing methods should be mandatory for any software, paragraph 1 Software Testing Plan - Tutorialspoint, paragraph 1