**The brief.** `RoundTo(value, digits)` just calls .NET's `Math.Round`. Simple — so you already know the answers, right? **Predict all eight outputs, then press Run.** Every ✗ is a place the code did something you did not expect. That gap is the whole point.

This is Module 1's discipline in miniature: before you trust code — or change it — pin what it actually does. When you write down what the code really does as a check that runs, you are writing a characterization test — a spec that records the code's true behaviour so you would notice the day it changes. It is the exact move you will make on real legacy code in Module 4 — Refactoring.

The rules

• The RoundTo function is fixed, and so are the inputs (Value, Digits). Only your predictions move.
• The Predicted column is pre-filled with the naive "round half up" guess. Some are right; most are not.
• Run, read the ✗ rows, and change each Predicted to match Actual until all eight say ✓. You have then pinned the behaviour.

No peeking at the solution until you have been surprised at least once — the surprise is the lesson.

Your workbench

When every row says ✓, you no longer believe what Math.Round does — you know, and you have written it down as a test that will catch the day it changes.

Been surprised enough? Reveal the solution — the same eight calls with their true outputs and the reason each one bites.

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