jschoubben
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Jochen asked whether the order made sense. It did not -- it followed when things happened to be decided, which after consolidation is fictional anyway since record 5 alone folds decisions taken across a week. Concretely wrong before: the domain statement sat at 8, after five engineering rules; the constitution was scattered across 5, 12 and 17; the tiers landed at 15, 16, 21 and 22 with process records in between. Now it walks: what the mesh is (1-3), its tiers from the bottom up (4-8), what runs on them and how it gets there (9-10), how it is built (11-16), how it is checked (17-18), how we work (19-23). Two things made this safe rather than free. It is a permutation, not a compaction, so the renames go through temporary names -- otherwise two files want one slot and one is lost. And the reference rewrite is a single simultaneous pass, because almost every number moved into a slot another number was vacating; replacing one at a time would have cascaded and pointed things at the wrong record while still resolving. Verified: 284 [ADR NNNN](path) links across the repository, all with matching text and target. The ordering principle is now stated in 19 rather than left implicit -- the repository already said "the numbering is the flow" about its folders, and there was no reason for the records to be the exception.
4.8 KiB
status, date, deciders, reconstructed
| status | date | deciders | reconstructed |
|---|---|---|---|
| accepted | 2026-08-24 | jochen | false |
17. A test defends a decision
Context
how-we-build.md §5 already says that if a document states a
rule about the mesh, it says how the rule is verified, on the grounds that an unenforced rule
is indistinguishable from a wrong one and costs more, because people believe it.
That rule is applied to prose and to acceptance criteria. It has never been applied to decisions, and it should be — a decision record states something that must be true, which is the same kind of claim.
The gap was found by review. The lab reached 2,128 lines with 1,072 of them untested, and
no stated rule was broken. There is no testing posture in how-we-build.md at all: no
expectation, no gate, no definition of done. Every decision the lab embodies — the underlay
boundary, the closed address space, routers as scenery, waiting for usable rather than for a
call to return — was verified by hand, by running scenarios and reading output, and none of
that survives the terminal it was run in.
Which is the fault the mesh already has catalogued at scale: an end-to-end harness that has
not built since 2026-06-04, and nothing said so
(04-ISSUES/005). Coverage
assumed rather than checked.
Considered options
- A coverage percentage. Rejected. It measures how much code a test touched, not whether anything important is defended, and it is satisfied by tests that assert nothing. A number would have been met by testing the parser harder while the hypervisor integration stayed unasserted.
- Test-driven development as a hard rule. Rejected, and not because it is wrong in general. Half the lab's implementation was discovery: that the hypervisor CLI reads a definition from stdin and hangs, that it assigns a MAC without recording it, that a stock image's boot-time networking flushes a static address. A test written first against undiscovered behaviour asserts a guess.
- A test defends a decision. Chosen.
Decision
Every decision record states something that must be true. A test asserts it.
A decision with no test is a decision that will quietly stop being true, and nobody will find out from a document. Concretely:
- Where a decision is about structure or logic — what a declaration may say, what is refused, how a name is derived — the test is a unit test, and it is written first, because the behaviour is knowable before the code.
- Where a decision is about behaviour against a real system — a hypervisor, a broker, a daemon — the test runs against the real thing, and is written alongside, because the behaviour is discovered rather than known.
- Mocking the boundary is forbidden. A test that fakes a hypervisor asserts that the fake behaves as expected, which is the shape of test this whole effort exists to stop shipping.
- The gate is blocking, and green is the definition of done. A change that has not run its tests is not finished, whatever its diff looks like.
A test names the decision it defends. Not as ceremony: it is what makes the pairing checkable, so a decision without one can be found rather than noticed.
Consequences
- The question "which tests matter" has an answer that is not a number. The decisions are the list, and they are already written down.
- A new decision costs a test. That is the intended friction — a decision nobody will assert is one worth reconsidering.
- Integration tests need real infrastructure and are slow. That cost is accepted: a fast test suite that mocks the boundary would tell us nothing about the boundary, which is where every interesting fault in this session actually was.
- Some decisions are not mechanically assertable — the mesh brokers capabilities; nodes host; agents think is a shape, not a predicate. Those should say so in the record rather than being quietly exempt, so the exemption is visible.
- Records 0001–0033 were made before this rule. They are not retroactively invalid, but each should acquire a test or an explicit note that it cannot have one, and until then this rule is aspirational for them — which is exactly the state §5 warns about, recorded rather than hidden.
References
how-we-build.md§5 — the rule this extends from prose to decisions.04-ISSUES/005— coverage assumed rather than checked, for two and a half months.- The sibling HQ repository for the PAPA platform states the same boundary rule — the contract is tested against the real system, mocking the client is forbidden, and a blocking gate is the definition of done. This record adopts that posture and adds the decision pairing.