Reject an impossible event
See this course’s project requirements
A tested fictional equipment-repair workflow with a transition table, guarded actions, rejected transitions and a trace of two complete cases.
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What to include
- A workflow map with distinct states and events.
- A complete allowed-transition table and a rejection case.
- A guarded verification matrix with accepted and rejected cases.
- An impossible-event test with state preservation.
- Complete, resumed and rejected workflow traces.
- A tested finite workflow model with honest completion boundaries.
Review and revise
Use these criteria to check your work and choose what to improve.
- The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
- Normal, boundary and rejected cases are recorded with expected versus observed results.
- The changed case has a correct explanation and does not rely on hidden state.
- The project includes source, outputs, instructions and honest tool, privacy and verification limits.
Want more background?
The idea in everyday life
Start new. Try close: ValueError. Keeping the caller’s state unchanged preserves new rather than mislabeling it closed.
Rejecting an impossible event protects historical meaning. The supplied function returns the next state but does not mutate the caller; assign a new state only after a successful call.
Reject an impossible event — original worked practice
Rejecting an impossible event protects historical meaning. The supplied function returns the next state but does not mutate the caller; assign a new state only after a successful call.
Start new. Try close: ValueError. Keeping the caller’s state unchanged preserves new rather than mislabeling it closed.
1. Step 1
Capture state=new before the call.
You should see: The baseline is clear.
This keeps the rule and its observable result together.
2. Step 2
Attempt transition(new, close).
You should see: The pair is absent and raises ValueError.
This keeps the rule and its observable result together.
3. Step 3
Assign next state only inside the success path.
You should see: Failure leaves the caller’s state as new.
This keeps the rule and its observable result together.
4. Step 4
Record the rejected action and unchanged state.
You should see: An impossible-event test with state preservation.
This keeps the rule and its observable result together.
What to finish
An impossible-event test with state preservation.
Watch for this
Returning the current state for every impossible event, hiding an invalid caller action.
How can I tell I understand it?
Explain and demonstrate the required distinction: Rejecting an impossible event protects historical meaning. The supplied function returns the next state but does not mutate the caller; assign a new state only after a successful call. Show a changed input and the expected result without weakening this contract.
Quick knowledge check
Answer all 3 questions. Get at least 2 right and the lesson completes automatically.
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Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.
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Sources and further reading
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Source & access notes · checked 2026-10-01
Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.
Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.
Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.
Source & access notes · checked 2026-10-01
Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.
Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.
Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.
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