# `mix corpus.coverage`
[🔗](https://github.com/riddler/predicator-ex/blob/v9.4.1/lib/mix/tasks/corpus.coverage.ex#L1)

Prints a checklist of behaviors the existing ExUnit suite exercises that
the shipped conformance corpus does not (`px-35i.4` Phase 6).

The corpus is authored JSON completed by the real pipeline, not extracted
from the suite (see `docs/plans/260807-px-35i.4-conformance-corpus.md`'s
"The generation mechanism" section) - so nothing else tells an author what
the 16k-line suite exercises that the corpus does not. This task closes
that loop, using the existing suite as an authoring checklist rather than
as the corpus's source of truth.

## What it does

1. Reads every `test/**/*.exs` file **except** `test/predicator/conformance/**`
   (the corpus's own test suite, not "the existing suite" this task
   checklists) and statically extracts literal `Predicator.evaluate/2,3` and
   `Predicator.compile/1` source strings via
   `Predicator.Conformance.Coverage.extract_sources/1`.
2. Compiles each extracted source through the real compiler and counts
   opcode/operand patterns via
   `Predicator.Conformance.Coverage.suite_pattern_frequencies/1`.
3. Reads the shipped `conformance/corpus/tier-*.json` cases and computes the
   same patterns via `corpus_pattern_frequencies/1`.
4. Diffs the two, keeping every pattern the suite hits more than the
   corpus.
5. Classifies each tier-5 (`call:<name>`) gap against the real builtin
   registry (`Predicator.Context.new().functions`'s keys) via
   `Coverage.classify/2`, and prints the result grouped by tier -
   `px-q1f`, so a test-registered function name (`boom`, `double`, ...)
   reads as "not a corpus candidate" rather than as an unauthored gap, and
   a non-deterministic builtin (`Date.now`, `Math.random`, same for the
   `relative_date` opcode) reads as a documented exclusion rather than a
   bare `corpus: 0`.

This is dev-only tooling: it never writes a conformance case, never touches
`conformance/cases/`, and never fails the gate - a wide report is expected
and is not itself a failure. It is a **heuristic** report (see
`Predicator.Conformance.Coverage`'s moduledoc for exactly what it can and
cannot see); its top entries need a human read before being authored as
cases, since some will still be Elixir-internal test scaffolding that
`classify/2`'s registry check does not catch (e.g. an opts-handling
assertion that happens to compile) rather than genuine corpus gaps.

## Usage

    mix corpus.coverage

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*Consult [api-reference.md](api-reference.md) for complete listing*