Error guessing uses experience, knowledge of common mistakes, and understanding of system weaknesses to hypothesize where defects may hide. It is a practical supplement to formal techniques rather than guesswork without a basis.
Sources of useful hypotheses
- →Defect history in the product or similar systems
- →Common development mistakes: null handling, off-by-one errors, role confusion, incorrect comparisons, and race conditions
- →Knowledge of complex integrations, unstable environments, and architectural weaknesses
- →Observations of especially vague requirements
Where it is useful
- →Exploratory testing and quick post-change checks
- →Areas where every scenario is difficult to formalize in advance
- →Defect investigations and searches for related problems
- →Smoke and sanity testing focused on likely failure areas
Applying it systematically
- →Record defect patterns and revisit them in later releases.
- →Distinguish useful hypotheses from random clicking.
- →Use error guessing alongside basic test design.
- →After finding a defect, ask which risk class belongs in ongoing coverage.
The main limitation
Relying solely on error guessing makes coverage uneven and dependent on one person's experience. Its strength is supplementing other techniques rather than serving as the only test design method.