> For the complete documentation index, see [llms.txt](https://ultimatewebsolutions.gitbook.io/qa-knowledge-base/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ultimatewebsolutions.gitbook.io/qa-knowledge-base/test-levels.md).

# Test levels

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### Unit Testing

Tests the smallest pieces of code: functions, methods, classes. Usually done by developers.
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### Integration Testing

Tests whether different components/modules work correctly together. 

Example: Frontend → API → database.
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Focus: interfaces and data flow between components.
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### System Testing

Tests the complete integrated application as a whole.
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Usually performed by QA. <br>

Example:&#x20;

Test an entire e-commerce flow: login → search product → add to cart → payment → order confirmation.
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### Acceptance Testing (UAT)

Determines whether the system meets business/user requirements and is ready for release. Usually performed by business users, product owners, or customers, with QA support.
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Example: Business verifies that an order can be created according to the defined business rules.
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{% hint style="info" %}
Smallest component → Components together → Whole system → Business acceptance
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