The correct order of TMMi maturity levels from low to high is:

Managed (Level 2): Testing becomes a managed and separate process from debugging, with formal strategies and plans.

Defined (Level 3): Testing is fully integrated into the development lifecycle, with standardized processes across projects.

Measured (Level 4): Testing processes are measured quantitatively, and product quality is evaluated with formal metrics.

This sequence reflects the increasing maturity and sophistication of an organization's testing processes as they progress through the levels.

TMMi Reference:

The TMMi maturity levels follow the order of Managed (Level 2), Defined (Level 3), and Measured (Level 4).