Each of the terms you mentioned is related to a different aspect of software testing and serves a specific purpose in the overall testing process. Here is a detailed breakdown of their differences:

Test Plan
It is as follows: A detailed blueprint outlining the scope, approach, resources, and timeline for planned testing activities.

The purpose of this document is to define what will be tested, how the testing will take place, who will perform the testing, and the timelines.

Details such as test objectives, deliverables, test environment setup, resource allocation, risk assessment, and so on are included in the content.

Audience members include test engineers, project managers, and stakeholders.

Test Strategy
What it is: A high-level document outlining the approach to be taken throughout the software testing life cycle.

The purpose of this document is to outline the overall plan for how testing will be approached at an organizational or project level, including the types of testing to be performed and the tools to be used.

Content: Provides an overview of general testing approaches, testing scope, resource allocation, and other high-level aspects. It is frequently consistent across projects.

Senior management, test managers, and stakeholders are the intended audience.

Test Methodology
It is as follows: The framework or philosophy that governs how testing will be carried out.

The goal of this document is to provide a set of guiding principles or practices for how testing should be conducted.

Agile, Waterfall, Spiral, Big Bang, and other methodologies may have their own distinct approaches to testing.

Everyone involved in the development and testing processes is the intended audience.

Design Technique
What it is: A set of procedures and methods for creating test cases.

The goal is to develop test cases that are effective and efficient at covering the test scope and detecting defects.

Examples include black-box and white-box testing, boundary value analysis, equivalence partitioning, and so on.

Audience: Primarily test engineers, but also developers and others involved in quality assurance.

Test Mitigation documents
What it is: A document outlining plans and strategies for mitigating the effects of testing risks.

The goal of this task is to identify potential risks during the testing process and to propose mitigation strategies for each identified risk.

Risk identification, risk impact analysis, and risk mitigation plans for each identified risk are included in the content.

Test managers, project managers, and stakeholders are the intended audience.

While all of these documents and terms have different purposes, scopes, and audiences, they are closely related and are frequently used in tandem to effectively and efficiently guide a project through its testing life cycle.