> ## Documentation Index
> Fetch the complete documentation index at: https://qodex.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# The four types of software testing

> A short, plain definition of the four levels of software testing (unit, integration, system, acceptance) and the functional versus non-functional split.

# The four types of software testing

Software testing is usually grouped into four levels, run from the smallest scope to the largest:

1. **Unit testing.** Checks one function or component in isolation. Fast, written by developers, close to the code.
2. **Integration testing.** Checks that units work together: a service calling its database, or one API calling another.
3. **System testing.** Checks the whole application end to end, the way it will actually run.
4. **Acceptance testing.** Checks that the finished system meets the requirements a user or business cares about.

A separate axis splits tests into **functional** (does the software do the right thing?) and **non-functional** (how well does it perform, for example speed, security, and usability). The four levels above are about scope; functional versus non-functional is about intent, and the two overlap.

## Where Qodex fits

Qodex focuses on functional testing at the integration, system, and acceptance levels for APIs and web apps, and it adds security testing, a non-functional concern, on the same suite. You describe what to test in plain English, an agent authors the scenarios, and they replay against your real running app. Unit tests, which sit closest to the code, stay in your own test framework.

## Related

<CardGroup cols={2}>
  <Card title="Functional testing" icon="list-checks" href="/docs/functional-testing">
    What functional testing checks, and how it differs from non-functional testing.
  </Card>

  <Card title="API testing" icon="plug" href="/docs/api-testing">
    How Qodex tests API behavior against a real environment.
  </Card>

  <Card title="UI testing" icon="monitor" href="/docs/ui-testing">
    How Qodex tests web apps in a real browser.
  </Card>

  <Card title="Security testing" icon="shield" href="/docs/security-testing">
    Continuous OWASP-aligned checks on the same suite.
  </Card>
</CardGroup>