Write data and UI acceptance cases — Build the smallest useful slice

PART I

Warm-up

Reconnect with a useful idea before starting write data and ui acceptance cases. In one or two sentences, describe the input, output or host boundary from the previous exercise that this lesson builds on. If you are arriving directly, skim the worked example first; there is no locked prerequisite.

A rough note is enough. You can revise it after the example.

PART II

Instruction & guided example

Build separate empty-success and unavailable states

Data and UI acceptance need the same concrete dataset. A report claim is testable only when the supplied rows, filter, projection, ordering and visible state are explicit. WDB’s proposed query design is not this website’s SQLite runtime. Field names and collections come from the exercise host, and tie, missing-value and snapshot rules need their own contracts.

Dataset r91 contains stocks 12 and 20, so stock<10 matches no rows. A second scenario supplies no dataset because the report service is unavailable. Both would otherwise render an empty table.

Calculate the selected rows by hand, then derive the visible representation from those results. Keep empty success separate from unavailable data. A screenshot can show a layout but cannot prove its underlying query or resource authorization was correct. Worked case: The first is a successful empty result: show No low-stock items in snapshot r91. The second has no query result: show Data unavailable and preserve any valid prior snapshot under its stale policy. Zero rows is not a substitute for missing data.

Compare the tempting alternative: Using an empty array for every service failure makes an outage look like healthy inventory and can mislead operational decisions.

Worked reasoning and supplied artifact

// Paper trace / supplied exercise-host contract; no execution claimed.
// Dataset r91 contains stocks 12 and 20, so stock<10 matches no rows. A second scenario supplies no dataset because the report service is unavailable. Both would otherwise render an empty table.
// The first is a successful empty result: show No low-stock items in snapshot r91. The second has no query result: show Data unavailable and preserve any valid prior snapshot under its stale policy. Zero rows is not a substitute for missing data.

Illustrative example from the proposed WillowScript design. The language and WUIX/WMATH/WDB/WAUDIO/WTMP services are not implemented in the supplied source. This site has no interpreter, VM or native host and does not execute or certify the snippet.

Try the guided change

Reconstruct the supplied worked case first: list its inputs, intermediate decisions and final artifact. Compare each row with the explanation and identify exactly where the rejected alternative fails. Then use the changed inputs in Part IV for independent work.

• Write the supplied inputs and initial state before following the example.
• Reconstruct each intermediate calculation or host decision, then compare with the worked artifact.
• Explain why the contrasting alternative fails before attempting the changed inputs in Part IV.

PART III

Take a breather

Step back after the guided example. Look away from the screen, stretch, or reread your prediction. This is an optional learning pause, not a timer or an assessment gate.

When you return, try to name the lesson’s key idea without copying its wording. If that feels difficult, return to Part II and trace one line rather than restarting the entire lesson.

PART IV

Independent practice

Project context: Operations reporting utility. Build a small, understandable change around write data and ui acceptance cases.

Specify status, row count, provenance and allowed actions for empty success, unavailable service and a normal matching result.

What to produce

A three-state report presentation table.

• State the intended behavior in a sentence before editing.
• Use only source-backed syntax and the host services whose contract you have been given.
• Record a normal case and a boundary or unavailable-resource case.
• Label hand predictions separately from anything actually measured in a supplied toolchain.

Syntax colors are a reading aid, not a compiler. The line you are editing stays uncolored until you move to a different line; capitalization is never changed. Drafts stay on this browser and code is not executed.

import wdb;
domain Inventory {
    const lowStock = wdb.query({
        from: products,
        select: [id, name, stock],
        where: [[ stock < 10 ]],
        order: { by: stock, direction: ascending }
    });
}

PART V

Self-check

Use this check to notice what to revisit. It does not award a private course grade, block another page or claim to verify compiled code. Every answer has a learning explanation.

You may keep exploring even if you are unsure. Use the hint, compare the trace, and revise your explanation.

PART VI

Recap & small task

Bring the idea back to the mod feature you are building. A useful recap connects the mechanism to a decision you can make in your own code.

• Build separate empty-success and unavailable states
• Specify status, row count, provenance and allowed actions for empty success, unavailable service and a normal matching result.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Write the message reserved for a confirmed empty result.

This marks your personal practice record only. It is not a certification or an official workspace assessment.