# Glossary

The vocabulary the method pages rely on: terms the project coins or
narrows, and the industry shorthand those pages assume.

For mappings to the wider testing vocabulary — *unit / integration / e2e*,
*mock* vs *stub* vs *fake*, *approval* ↔ *snapshot* ↔ *golden
master*, *classicist* vs *mockist* — see
[Conventional terminology](https://quality.stereobooster.com/terminology.md).

## Project terms

- **Oracle.** Anything that decides whether an output is correct.
  In an example test, the oracle is the author's expected output
  hard-coded in the assertion. In property-based testing, the
  oracle is a property. In differential testing, the oracle is
  another implementation. In metamorphic testing, the oracle is
  a relation. In fuzzing with a sanitizer, the oracle is the
  sanitizer.
- **Effect.** What the code under test *touches* — the [code
  axis](https://quality.stereobooster.com/effect.md); it determines which verification method fits. Inspired
  by Koka's effect rows, but regrouped for testing, with nondeterminism split
  into magnitude tiers.
- **Effect scope.** A method's *effect ceiling*: the richest code-effect
  (state, I/O, nondeterminism tier) it can verify faithfully without quietly
  reducing the system. The [Effect axis](https://quality.stereobooster.com/effect.md) read method-side: for
  code with a given effect, the adequate methods are those whose scope covers
  it. A separate question from how much of its space a run exercises
  (*reachability*) and how strong a claim a pass makes
  ([guarantee](https://quality.stereobooster.com/guarantee.md)).
- **Effectiveness.** A test suite's ability to detect faults — the
  field's term for "how good are the tests." It decomposes through the
  *RIPR* chain and behaves like a product, so a coverage percentage (one
  factor) is a poor proxy. See [measuring test-suite
  effectiveness](https://quality.stereobooster.com/measuring-test-effectiveness.md).
- **RIPR.** Why a test catches a fault, in four steps; coverage reads only the
  first, the oracle is the last, and mutation testing exercises the whole chain
  (see [measuring test-suite
  effectiveness](https://quality.stereobooster.com/measuring-test-effectiveness.md)):
    - *Reachability*: the test executes the faulty code.
    - *Infection*: executing it produces a wrong program state.
    - *Propagation*: the wrong state reaches an observable output.
    - *Revealability*: the oracle checks that output.
- **Adequacy.** Criterion-relative thoroughness: a suite is "X-adequate"
  if it satisfies criterion X (statement, branch, MC/DC, mutation). The
  *adequacy ladder* orders criteria by demandingness and refines the
  [guarantee](https://quality.stereobooster.com/guarantee.md) axis.
- **Reachability.** Whether a run executes the code, path, or state in question:
  what [coverage](https://quality.stereobooster.com/coverage.md) measures, and the first factor of
  *RIPR*. Also the refinement beneath the [guarantee](https://quality.stereobooster.com/guarantee.md)
  tier: how much of a method's own space a run exercises. Distinct from a
  method's *effect scope* (which effects it covers, not how much of them).
- **Guarantee.** The strength of claim a passing run licenses (also said it
  *warrants*, *underwrites*, or *vouches for* the claim): a per-method tier
  ordered by soundness, from a guess to a proof. Capped by the input and oracle
  axes and refined by adequacy. See [guarantee](https://quality.stereobooster.com/guarantee.md).
- **Predicate.** A boolean function of a value ($x > 0$) — the
  position-neutral atom beneath several named roles. As a *shape*
  constraint it is a **type** ($x : T$); a *precondition*,
  *postcondition*, *invariant*, *property*, *constraint*, or
  *refinement* is the same predicate placed at a position or
  discharged a particular way. See
  [contracts as specifications](https://quality.stereobooster.com/contracts-as-specifications.md).
- **Invariant.** Overloaded across communities; each sense means *holds constant
  as something varies*, and the same word names different cuts (the oracle-axis
  sense $f(x) \geq 0$ is, in contract terms, a *postcondition*, not the lifetime
  invariant; see [contracts as specifications](https://quality.stereobooster.com/contracts-as-specifications.md)):
    - **Across inputs**: on the [oracle axis](https://quality.stereobooster.com/oracle.md) and in
      property-based testing, a predicate that holds for every input,
      $\forall x.\ P(f(x))$ (`sort(xs)` is ordered).
    - **Across a lifetime**: in Design by Contract, a predicate on an object's
      state, holding before and after every public method.
    - **Across iterations**: in Hoare logic, a loop invariant.
- **Regression ceiling.** The structural limit on what
  example-based tests can catch: *example tests guarantee the
  absence of known bugs, not the absence of bugs* — see
  [Example tests](https://quality.stereobooster.com/example-tests.md).
- **Ceiling-breaking method.** Any method whose oracle isn't the
  test author's intuition: property-based testing, fuzzing,
  differential testing, metamorphic testing, formal methods,
  types, contracts. Defined opposite to *example-based*; framing
  in [Example tests](https://quality.stereobooster.com/example-tests.md).
- **Hygiene tool.** A tool that improves consistency without
  reasoning about runtime behavior: formatters, stylistic lint
  rules, naming conventions. Useful but **not verification**.
- **Verification method.** A tool or practice that reasons about
  runtime behavior. Types, contracts, tests of all kinds,
  formal methods, code review, runtime monitoring, fuzzing.
- **Soundness** and **completeness** (analysis). *Sound*: no false negatives
  within scope, so the analysis never reports "ok" when the bug it targets is
  present. *Complete*: no false positives, never flagging a non-bug (the dual).
  A tool is usually one, not both. This is the program-analysis property behind
  the [guarantee](https://quality.stereobooster.com/guarantee.md) tiers. See
  [abstract interpretation](https://quality.stereobooster.com/abstract-interpretation.md)
  and [termination analysis](https://quality.stereobooster.com/termination-analysis.md).
- **Sound type system** vs **unsound type system.** A type
  system is *sound* if a passing check guarantees the absence of
  the type errors the system claims to forbid. Haskell and OCaml
  are sound (within their expressive reach). TypeScript and mypy
  are *unsound by design* — gradual typing keeps backward
  compatibility with dynamic code. See
  [Static types](https://quality.stereobooster.com/static-types.md).
- **By construction.** Of a guarantee: holds because of the
  structure of the code or the verifier, not because we observed
  it on test inputs. Memory safety in Rust is *by construction*;
  memory safety in C with AddressSanitizer is *empirical*.
- **Folklore.** The project's evidence tier for claims that
  are widely cited but unsupported by primary studies. Parallel
  categories:
    - [Testing folklore](https://quality.stereobooster.com/testing-folklore.md):
      the pyramid as prescription, the 80% coverage target, TDD as
      universal design discipline, the 5–8× PBT productivity multiplier,
      "100% coverage subsumes types".
    - [Design folklore](https://quality.stereobooster.com/design-folklore.md):
      small files as a universal prescription, cyclomatic complexity as a
      quality KPI, GoF patterns as a universal design vocabulary, DRY as
      no duplication.

## Industry shorthand

Terms with a settled meaning across the engineering literature.
The method pages use them without further definition.

- **Shift-left.** Move quality work earlier in the development
  cycle, where defects are cheaper to fix. The framing dates to
  Fagan-era inspection literature and pre-dates "shift-left" as
  a marketing term.
- **TDD** — test-driven development. Red-green-refactor cycle.
  The project treats TDD's empirical record as *mixed*; the
  "TDD as universal design discipline" section in
  [Testing folklore](https://quality.stereobooster.com/testing-folklore.md)
  carries the case-by-case analysis.

## Referenced by

- [Contracts as specifications](https://quality.stereobooster.com/contracts-as-specifications.md) · Methods
- [Software Quality](https://quality.stereobooster.com/index.md) · Overview

## Acronyms

- DRY — don't repeat yourself
- KPI — key performance indicator
- MC/DC — modified condition/decision coverage
- PBT — property-based testing
- RIPR — reachability, infection, propagation, revealability
- TDD — test-driven development