decision-table

List all input conditions and possible actions, build a table where each column is one condition combination mapped to actions, then create at least one test case per rule. Merge rules that share actions using don't-care entries to reduce the table.

Use decision table testing when system behavior depends on the simultaneous combination of multiple conditions, such as nested if-else logic. Equivalence partitioning and boundary value analysis suit single-variable inputs but miss condition interactions.

A table with N binary conditions has at most 2^N rules. After reduction with don't-care entries and removal of impossible combinations, the practical number of rules and test cases is usually much smaller.

A don't care entry, marked with a dash, means a condition does not affect the action for that rule. It lets you merge rules that produce identical actions, reducing the total number of test cases needed.

Impossible rules are condition combinations that cannot occur in reality, such as a correct password for an email that does not exist. They should be explicitly identified, documented with the reason for exclusion, and removed from the table.