Confusing these three terms in the C1-2 writing test or C1-3 interview drops marks instantly — Testing and Validation both live in Development, while Evaluation is its own stage.

| Term | PSM stage | Purpose | Concrete example |

**Example:** Enter `25` into an age field and expect a calculated result. If the output matches the design, the test passes. If the program crashes or returns the wrong value, testing has found a bug to fix.

Validation checks that **data entered by the user is reasonable** before the program processes it. It runs at the point of input — not after — and prevents garbage data from reaching the rest of the program. Like testing, validation is part of the **Development** stage.

**Example:** The age field should reject `−3`. Validation code checks for this (`if age < 0: display error`) and stops the bad value from being used in any calculation.

Evaluation judges whether the **completed solution meets the evaluation criteria** set during the Design stage. It is PSM Stage 4 — separate from Development. You are not checking individual inputs or features; you are assessing the solution as a whole against measurable standards.

**Example:** "Does the finished app allow 90% of beta testers to complete onboarding in under 2 minutes?" That criterion was written in Design. Evaluation collects evidence (surveys, observation, usage data) and checks whether it was met.

The C1-2 writing test and C1-3 interview both probe PSM knowledge directly. A question like "which Development activities does your project plan include?" expects you to name validation, testing, and documentation separately — not lump them together. At the C1-3 interview you may be asked to point to evidence of each activity in your GitHub Projects board. If your plan only shows "testing" with no separate validation tasks, that signals a gap. At Stage 4, markers check that you are measuring against your Design-stage criteria, not just describing whether the app runs.

- [Problem-Solving Methodology](/sd/C01/Problem-Solving%20Methodology)