What testing design techniques do you know and which ones have you used most often?

Among test design techniques, the following can be distinguished:

• Equivalence partitioning — dividing input data into equivalence classes to test one representative from each class.
• Boundary value analysis — testing values at the edges of ranges where errors often occur.
• Decision tables — using tables to systematize conditions and expected results.
• States and transitions — modeling system behavior through states and transitions between them.
• Error-oriented testing — focusing on typical errors and exceptions.

In work, I most often used equivalence partitioning and boundary value analysis, as they are simple and effective for most tasks.