5.2.2 Test Strategy and Test Approach

A test strategy provides a generalized description of the test process, usually at the product or organizational level. Common types of test strategies include:

• Analytical: This type of test strategy is based on an analysis of some factor (e.g., requirement or risk). Risk-based testing is an example of an analytical approach, where tests are designed and prioritized based on the level of risk.

• Model-Based: In this type of test strategy, tests are designed based on some model of some required aspect of the product, such as a function, a business process, an internal structure, or a non-functional characteristic (e.g., reliability). Examples of such models include business process models, state models, and reliability growth models.

• Methodical: This type of test strategy relies on making systematic use of some predefined set of tests or test conditions, such as a taxonomy of common or likely types of failures, a list of important quality characteristics, or company-wide look-and-feel standards for mobile apps or web pages.

• Process-compliant (or standard-compliant): This type of test strategy involves analyzing, designing, and implementing tests based on external rules and standards, such as those specified by industry-specific standards, by process documentation, by the rigorous identification and use of the test basis, or by any process or standard imposed on or by the organization.

• Directed (or consultative): This type of test strategy is driven primarily by the advice, guidance, or instructions of stakeholders, business domain experts, or technology experts, who may be outside the test team or outside the organization itself.

• Regression-averse: This type of test strategy is motivated by a desire to avoid regression of existing capabilities. This test strategy includes reuse of existing testware (especially test cases and test data), extensive automation of regression tests, and standard test suites.

• Reactive: In this type of test strategy, testing is reactive to the component or system being tested, and the events occurring during test execution, rather than being pre-planned (as the preceding strategies are). Tests are designed and implemented, and may immediately be executed in response to knowledge gained from prior test results. Exploratory testing is a common technique employed in reactive strategies.

An appropriate test strategy is often created by combining several of these types of test strategies. For example, risk-based testing (an analytical strategy) can be combined with exploratory testing (a reactive strategy); they complement each other and may achieve more effective testing when used together.

While the test strategy provides a generalized description of the test process, the test approach tailors the test strategy for a particular project or release. The test approach is the starting point for selecting the test techniques, test levels, and test types, and for defining the entry criteria and exit criteria (or definition of ready and definition of done, respectively). The tailoring of the strategy is based on decisions made in relation to the complexity and goals of the project, the type of product being developed, and product risk analysis. The selected approach depends on the context and may consider factors such as risks, safety, available resources and skills, technology, the nature of the system (e.g., custom-built versus COTS), test objectives, and regulations.