Test Strategy is also known as test approach defines how testing would be carried out. Test approach has two techniques:
Proactive - An approach in which the test design process is initiated as early as possible in order to find and fix the defects before the build is created.
Reactive - An approach in which the testing is not started until after design and coding are completed.
There are many strategies that a project can adopt depending on the context and some of them are:
Dynamic and heuristic approaches
Model-based approach that uses statistical information about failure rates.
Approaches based on risk-based testing where the entire development takes place based on the risk
Methodical approaches which is based on failures.
Standard-compliant approach specified by industry-specific standards.
Risks of product or risk of failure or the environment and the company
Expertise and experience of the people in the proposed tools and techniques.
Regulatory and legal aspects, such as external and internal regulations of the development process
The nature of the product and the domain