You already know the difference between a unit test and an integration test. The real challenge isn't in defining the test types, but in deciding how many of each to write. A solid test strategy is a plan for how you'll invest your testing effort to get the most confidence in your software with the least amount of friction. It's about balancing speed, cost, and coverage.

Think of it like building a house. You need a strong foundation, solid walls, and a reliable roof. Each part serves a different purpose, and you can't just build a house that's all foundation or all roof. Your test suite is the same. Two popular blueprints for structuring this effort are the Test Pyramid and the Testing Trophy.

The classic Test Pyramid, popularised by Mike Cohn, advocates for a large base of unit tests. These are fast, stable, and cheap to run. They check small pieces of logic in isolation. The middle layer has fewer integration tests, which verify that different parts of your system work together correctly. At the very top, you have a small number of end-to-end (E2E) tests that simulate a full user journey through the application. This model prioritises fast feedback and pinpoints failures precisely at the unit level.

However, the landscape has changed. Modern applications often rely heavily on integrating third-party services and complex front-end frameworks. This led to a different strategic model: the Testing Trophy, proposed by Kent C. Dodds. This model gives more importance to integration tests.

The Testing Trophy argues that the greatest return on investment comes from integration tests. These tests provide high confidence that your application works as intended without the brittleness and slowness of full E2E tests. Unit tests are still the foundation, but they form a smaller part of the overall strategy. The goal is to write tests that resemble how your software will actually be used.

Choosing between the Pyramid and Trophy isn't about right or wrong; it's about context. Your decision should be driven by risk analysis and clear objectives.

A [{] approach helps you focus your efforts where they matter most. Instead of trying to test everything equally, you prioritise based on the likelihood and impact of potential failures. Ask your team: What's the most critical user journey? Which feature, if it breaks, would cause the most damage to the business or users? Where is the code most complex or prone to change? The answers will guide where you should concentrate your more expensive integration and E2E tests.

This leads to defining clear test objectives. A good objective is specific and measurable. Instead of "test the login page," a better objective is "verify that a registered user can log in with valid credentials, and an unregistered user is shown an appropriate error message."

From these objectives, you define your exit criteria—the conditions that must be met for testing to be considered complete. This isn't about finding every single bug. It's a pragmatic agreement on what level of quality is acceptable for release. For example, your exit criteria might be:

• 100% of critical-path test cases have passed.
• No known high-priority bugs are outstanding.
• Code coverage from unit tests is above 85%.

By defining these elements upfront, you transform testing from a vague activity into a structured, goal-oriented process. Your strategy provides a clear roadmap, ensuring that every test you write contributes directly to building a high-quality product that meets business needs.

Building a test strategy is a core skill that separates good engineers from great ones. It requires thinking beyond individual tests to see the bigger picture of quality, risk, and business value.