Decision Testing
Decision testing is a white-box test technique that designs tests to execute every possible outcome of program decisions.
“A white-box test technique in which test cases are designed to execute decision outcomes.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Decision Testing?
Decision testing focuses on the control flow created by conditional statements to ensure each decision behaves correctly.
Decision logic: Every true and false outcome is exercised.
Structural approach: Test cases are derived from program structure.
Coverage objective: Supports achieving decision or branch coverage.
Real World Example
A loan approval function contains a single decision: if the applicant's credit score is 650 or above, approve; otherwise, reject.
A previous round of testing ran one applicant who got approved, and the coverage tool reports 100% statement coverage — but the reject branch has never actually executed, so the team has no evidence about what happens on that outcome.
The tester designs Decision testing by identifying the decision point and deliberately choosing an applicant just below 650, forcing the reject outcome to execute, so that both the true and false outcomes of the decision are exercised, not just one line inside it.
Running the reject branch for the first time reveals that declined applicants were shown "approved" in their confirmation email due to a copy-paste bug — a defect the earlier statement-coverage-only testing had completely missed, because that branch had simply never run.
Practice Questions
Question 1
A loan approval function's if/else is tested only with applicants who get approved, and the coverage tool reports 100% statement coverage. What has NOT necessarily been achieved?
Question 2
Which test design approach BEST achieves decision coverage for an if/else statement?
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