Testing

What tests can tell us about a system, what their limits are, and how they help evaluate its quality.

What characterizes a unit test, what isolating a unit means, and how to keep the test from depending too much on the implementation.

Five criteria for writing tests that are fast, independent, and repeatable, with clear results and written at the right moment.

Set up the scenario, run an action, check the result. How to use Arrange, Act, Assert to write tests that are easy to follow.

What role each kind of double plays and how to pick the right one for controlling a test's dependencies.

How the cycle of writing a test, making it pass, and refactoring guides the implementation and helps you review the design.

What problems show up when you connect components, and how to test those interactions beyond unit tests.

How to evaluate the behavior of the complete system, and how it differs from testing the integration between components.

Meeting a specification doesn't guarantee the system answers the business's needs. How to evaluate its acceptance, and who takes part.

How to evaluate response times and capacity under different loads, without relying on averages alone.

How to evaluate access controls and find vulnerabilities with tests and static and dynamic analysis. What each approach contributes.

How to evaluate whether people can understand and use the system, and how it differs from other UX research activities.

How to verify that software works in the environments you support, and that its changes keep the backward compatibility you need.