We split testing into distinct stages primarily because:
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) It is easier to manage testing in stages
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We can run different tests in different environments
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Each test stage has a different purpose.
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The more stages we have, the better the testing.
Testing is split into stages because each stage serves a distinct purpose: unit testing verifies individual components, integration testing checks interfaces, system testing validates the complete system, and UAT confirms business requirements. This is NOT about manageability, different environments, or maximizing stage count. The different purposes (component-level vs system-level vs user-level) are fundamental.
Testing is broken into stages (unit, integration, system, acceptance, etc.) because each stage targets a distinct objective — for example checking a component in isolation versus checking how the whole system behaves end-to-end. Splitting stages isn't about ease of management or piling on more stages for its own sake; it's about giving each stage a focused goal so defects are caught at the cheapest, most appropriate point.