How does component testing differ from E2E?

Component testing and E2E testing check the interface at different levels.

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#What a component test checks

• One specific component in isolation
• Its rendering, state and reaction to actions
• Behavior with different props and events

Focus: a small, controlled fragment of the UI.

The question it answers: "Does this component work correctly on its own?"

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#What an E2E test checks

• A complete user scenario from start to finish
• The interaction of many components, APIs, routes, data and pages at once
• The real operation of the application in the browser

Focus: the behavior of the whole system through the user's eyes.

The question it answers: "Can the user complete the task without errors?"

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#The key difference in scale

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#The main idea

• Component testing protects the UI building blocks
• E2E protects user scenarios

Both approaches are needed, but they complement rather than replace each other.