Quality Assurance Software Testing levels:

Testing is applied to different types of targets, in different stages or levels of work effort. These levels are distinguished typically by those roles that are best skilled to design and conduct the tests, and where techniques are most appropriate for testing at each level. It's important to ensure a balance of focus is retained across these different work efforts.

Developer Testing
Developer testing denotes the aspects of test design and implementation most appropriate for the team of developers to undertake. In most cases, test execution initially occurs with the developer-testing group who designed and implemented the test, but it is a good practice for the developers to create their tests in such a way so as to make them available to independent testing groups for execution.

Independent Testing
Independent testing denotes the test design and implementation most appropriately performed by someone who is independent from the team of developers. In most cases, test execution initially occurs with the independent testing group that designed and implemented the test, but the independent testers should create their tests to make them available to the developer testing groups for execution.

The other levels include:
Independent Stakeholder Testing- testing that is based on the needs and concerns of various stakeholders
Unit testing - Unit testing focuses on verifying the smallest testable elements of the software.
Integration testing - to ensure that the components in the implementation model operate properly when combined to execute a use case.
System Testing - Usually the target is the system's end- to-end functioning elements
Acceptance Testing - to verify that the software is ready, and that it can be used by end users to perform those functions and tasks for which the software was built.