Test Strategy in software testing is defined as a set of guiding principles that determines the test design & regulates how the software testing process will be done. 

A Test Plan is defined as a document that outlines the scope, objective, method, and weight of a software testing task in a project.

• A test strategy is carried out by the project or test manager with the collaboration of the test team.
• The test plan is carried out by a testing manager, lead, or the tester(s) of the project.
• The test plan can be changed during the project, for example, once in every iteration. While test strategy should not be changed very often.
• The test plan describes the details. While test strategy describes the general methodologies.