Unit 9 — Software Testing

Learning objectives

• Design tests at unit, integration, system, and acceptance levels.
• Apply equivalence partitioning, boundary analysis, and negative testing.
• Use test doubles appropriately and interpret coverage critically.

Testing is information production

A test is valuable when it can reveal a meaningful fault or reduce uncertainty about important behavior.

Test pyramid as a heuristic

flowchart TB
    E2E[End-to-end tests: few, high realism]
    INT[Integration/service tests: some]
    UNIT[Unit tests: many, fast, focused]
    E2E --> INT --> UNIT

The exact shape varies by system. The principle is to obtain useful feedback at reasonable cost and speed.

Boundary example

For an input allowed from 1 through 100, useful values include 0, 1, 2, 99, 100, and 101—not only a typical value such as 50.

Coverage

Coverage can reveal unexecuted code, but 100% statement coverage can still miss incorrect assertions, missing requirements, interaction faults, and security problems.

Tip

A strong test suite should fail for the right reason when the relevant behavior is intentionally broken.