---
title: Axis 09 · Vacancy: Did the test even reach the rule?
description: Axis 09, Vacancy: Did the test even reach the rule?
url: https://docs-v3-preview.elastic.dev/axes/09-vacancy
---

# Axis 09 · Vacancy: Did the test even reach the rule?
## In plain words

A smoke alarm test where nobody lit a match. The alarm did not go off, and the test passed, and you learned nothing. A test is *vacuous* when the data never reached the rule it was supposed to check.

## The bug you would ship

Every rule held and the suite was green. But the generator only made pending orders, so the rule about confirmed orders was never checked. A green run, and no evidence at all.

## You declare

You declare nothing. This axis is automatic, and it runs on every other axis.

## The library does

It checks that every rule *can* fire (it finds or is given a value that breaks the rule, and only that rule). It checks that a rule that applies "when X" saw an X. And each other axis checks its own version of the same thing: the operation changed something, the value moved, an order had two items, a run passed the deadline.

## When it fails, you read

Vacancy: the test passed without proving anything.
Rule                   confirmed-orders-have-lines
Not exercised because  its guard was never true for the 200 generated values, so the rule held without being exercised.
Next                   give the auto-test starts where the guard is true (for example a generator that sometimes draws the case the guard names), or mix such values into it.
Law                    Every rule can fire, and every rule's guard is reached by the data the tests use.
Consequence            A rule that can never fire, or a test that never reached it, reports green while checking nothing.
How to read this:
- **Rule** names the rule that was never exercised, and **Not exercised because** says why.
- **Next** says what to change, usually the generator, so the data reaches the rule.


## Why you did not write this test

This is the one that makes the other eight trustworthy. A property test that passes has not told you the property holds; it has told you it did not find a counter-example. If it never looked, that means nothing.

## In real code

In docs-builder, this axis found that the changelog entry generator never produced a marker entry, so none of the marker rules had ever run.
---

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