Which testing do you consider the most important: Smoke, Sanity, or Regression?

Each testing has its own critical importance depending on the context and stage of development. However, if I had to choose one, I would highlight Smoke testing as the first and fundamental in importance.

Why Smoke testing is the most important:

1. Early detection of critical defects: It quickly checks the basic operability of the main functions of the system after build or deployment.
2. Cost prevention: It allows rejecting non-functional builds early on, before conducting more in-depth and costly types of testing (Sanity, Regression).
3. Time and resource saving: If the Smoke test fails, there is no point in spending time and effort on further testing of a obviously defective build.

Sanity testing is important after minor changes or bug fixes to ensure that the changes work correctly and did not break related parts.

Regression testing is critical to ensure system stability and the absence of side effects after implementing new features, fixing defects, or making changes in the code.

Thus, Smoke testing acts as a "guard" for the build, allowing quick decision-making on further steps. Without successful completion of the Smoke test, it makes no sense to proceed to Sanity or Regression.