Equivalence Partitioning
Dividing input data into groups (partitions) where all values in a group should behave the same way.
Full definition
Equivalence partitioning (EP) is a black-box test design technique that divides input data into groups (partitions) where all values within a partition are expected to produce the same behavior. You then test one value from each partition instead of testing every possible value.
Example — Age field (valid range: 18-65):
- Partition 1 (invalid): < 18 → test with 15
- Partition 2 (valid): 18-65 → test with 30
- Partition 3 (invalid): > 65 → test with 70
Instead of testing ages 1, 2, 3... 100, you test 3 representative values. This reduces the number of test cases while maintaining good coverage.
Types of partitions:
- Valid partitions: Expected input the system should accept
- Invalid partitions: Input the system should reject
EP is often combined with Boundary Value Analysis for more thorough coverage. This is a core ISTQB topic.
Interview tip
Be ready to apply EP to any input field. Practice with examples: email field, phone number, quantity field.