Adding a Statistical Test

Audience: internals contributors adding a new TEST_* operator — tier-1 (row-stream) or tier-2 (post-test on the materialised result set).

The recipe mirrors the aggregator and feature recipes; the test-specific moving parts are streamability, the test catalog, and the registered-test capability table.

From CLAUDE.md, “Update Demand” rows for statistical tests and tier-2 post-test variants.

1. Decide tier

• Tier 1. Runs against the raw row stream, alongside aggregators. Online-moments tests (TEST_T, TEST_WELCH, TEST_CHISQ, TEST_ANOVA_F) stay in the streaming Process path. Sort-required tests (TEST_KS) force the buffered path.
• Tier 2. Runs after the result set is materialised, in req.PostTests. Always buffered.

2. Declare the type constant

Add to types/types.go:

const (
    // ... existing constants ...
    TEST_GINI_TREND TestType = "TEST_GINI_TREND"
)

Add it to types.AllTestTypes().

3. Implement and register

Tests live in processing/test_*.go. Existing examples to mirror:

• processing/test_t.go — online tier-1 test.
• processing/test_anova.go — tier-1 ANOVA with grouper support.
• processing/test_post.go and processing/test_post_more.go — tier-2 post-tests.
• processing/test_studentized.go — numerical integration utilities (used by TEST_TUKEY_HSD).

Register the test in processing/test.go (the registry construction calls). For tier-2 variants, declare both the base type and the variant identifier the post-test surface uses.

4. Streamability

Add a case in types/streamability.go for the new TestType:

func (t TestType) Streamable() bool {
    switch t {
    // ...
    case TEST_GINI_TREND:
        return false // sort-based
    }
}

Add the matching row in types/streamability_test.go so TestStreamability_TestsKnown passes.

5. Capability declaration

Add a row to descriptor/capabilities_tests.go:

• For a tier-1 test, declare it in the tier-1 catalog (testCapabilities).
• For a tier-2 post-test, declare it in postTestCapabilities.

TestManifestTestsComplete and TestManifestPostTestsComplete enforce that the manifest enumerates every registered test.

6. Skill update

Add an entry to skills/statistical-testing.md under “Operator catalog”. Describe the test’s family, inputs, outputs (statistic, p, df, effect size, …), and any preconditions (PULSE_TEST_* error codes it can raise). For tier-2 variants, also document the variant field shape since the post-test API exposes it.

7. Tests

Use the same TDD pattern as for aggregators. The processing package has rich existing test files to model new cases against: processor_test_pipeline_test.go, test_parametric_test.go, test_nonparametric_test.go, test_post_more_test.go. Add hermetic fixtures that exercise the streaming and buffered paths.

8. Error codes

If your test introduces a new failure mode, add a code to errors/codes.go (mirror the existing PULSE_TEST_* family), register its description row in descriptor/capabilities_errors.go, and document recovery in skills/error-code-reference.md. See the Adding an Aggregator recipe for the same pattern at the aggregator layer.

9. CLAUDE.md

Update CLAUDE.md’s “Current registered components → statistical tests” line with the new operator. If the test introduces a new preconditions class (e.g. paired sample, repeated measures), also add a sentence describing it in the parent paragraph.

10. Run the gates

go test ./processing/ -run TestType_Streamable
go test ./types/    -run TestStreamability_TestsKnown
go test ./descriptor/ -run TestManifest
go test ./skills/    -run TestSkillsCoverAll
go test ./...

See The Update Demand for the full row that governs statistical-test changes.