When you consider the place of usability testing in the overall product development process, then there are two main types of usability test: formative testing and summative testing.
Formative testing takes the role of support tool for decision making during the first stages of the design process and provides valuable insights where users have difficult reaching their user goals with the product.
Formative testing are carried out:
- During the development of the product.
- To improve the product.
- Virtually everywhere, yo do not need a lab.
The outputs of a formative testing may include:
- Participant comments in the form of a "thinking aloud" narrative.
- Usability problems and suggested fixes.
- Photographs and highlights videos.
In a typical project, you will conduct two formative testings: One in the early concept stage where the UX may be captured as paper prototype. The second happens when early versions of the software are available to catch issues right at the beginning of the development stage.
Summative testing is a QA type of test performed later in the product development process. The only difference is the stage of the development.
It provides metrics like task success, error rate, and user satisfaction. The pass/fail metric is the most important measurement in this type of test.
Summative testing is carried out:
- At the end of a development stage.
- To measure or validate the usability of a product.
- To answer the question: "How usable is this product".
- To compare against competitor products or usability metrics.
- With the participant working alone.
In most cases, we see summative testing more clear. It provides insights to apply via iteration.
My recommendation is to have at least one formative test, and of course, lot of summative test to iterate and improve design.