red

TDD Red Phase

You are now in the Red Phase of TDD. Follow these instructions to activate ONE test and make it fail.

Your Mission

1. Activate exactly ONE test from the test list
2. Make explicit predictions about how it will fail
3. Verify the test fails for the right reason
4. Maintain strict discipline - NO implementation during Red phase

Context: $ARGUMENTS

Red Phase Rules

• One test at a time: Convert exactly ONE it.todo() to executable test
• All other tests remain as it.todo(): Never have more than one failing test
• Two-stage failure: First compilation error, then runtime/assertion error
• Make predictions: Explicitly state expected failures before running tests
• No implementation: Don't write code to make test pass yet

Process

Step 1: Activate One Test

Identify the next it.todo() and convert it to executable test code:

// Convert from:
it.todo("should return 0 for empty input");

// To:
it("should return 0 for empty input", () => {
  expect(calculate("")).toBe(0);
});

Leave all other tests as it.todo().

Step 2: Predict Compilation Error

Before running the test, state your prediction:

🔴 Red Phase - Compilation Error Prediction:
- Test: "should return 0 for empty input"
- Expected: Compilation error
- Reason: Function `calculate` doesn't exist yet
- Error: "Cannot find name 'calculate'"

Step 3: Run Test - Verify Compilation Error

Run npm test and verify:

• ✅ Compilation error as predicted, OR
• ❌ Prediction wrong → follow the Prediction Failure Protocol below

Step 4: Create Empty Function

Create minimal function stub (no logic):

export const calculate = (input: string): number => {
  return undefined as unknown as number; // Intentionally wrong
};

Step 5: Predict Runtime Error

Before running again, state your prediction:

🔴 Red Phase - Runtime Error Prediction:
- Test: "should return 0 for empty input"
- Expected: Runtime assertion error
- Expected value: 0
- Actual value: undefined
- Diff:
  Expected: 0
  Received: undefined