---
phase: 03-expansion-engine
plan: "03"
subsystem: testing
tags: [proptest, property-based-testing, sql-generation, group-by, join-pruning]

# Dependency graph
requires:
  - phase: 03-expansion-engine
    plan: "01"
    provides: "expand() function, QueryRequest, ExpandError, quote_ident()"
  - phase: 03-expansion-engine
    plan: "02"
    provides: "Join resolution with source_table pruning, fuzzy matching"
provides:
  - "6 property-based tests verifying expansion invariants for arbitrary dim/metric subsets"
  - "proptest dev-dependency and integration test infrastructure"
  - "lib crate-type enabling integration tests for cdylib crate"
affects: [04-query-interface, 05-hardening-and-docs]

# Tech tracking
tech-stack:
  added: [proptest 1.9]
  patterns: [property-based-testing, subsequence-strategy, integration-test-fixtures]

key-files:
  created: [tests/expand_proptest.rs]
  modified: [Cargo.toml]

key-decisions:
  - "Added lib to crate-type alongside cdylib to enable integration tests (cdylib alone cannot be linked by test binaries)"
  - "Used proptest::sample::subsequence for generating valid dimension/metric subsets from definitions"
  - "Default proptest config (256 cases per property) is sufficient for the dimension/metric subset space"

patterns-established:
  - "Integration test fixtures: simple_definition() (no joins) and joined_definition() (with joins) for reuse"
  - "arb_query_request() strategy pattern for generating valid QueryRequest from any SemanticViewDefinition"

requirements-completed: [TEST-02]

# Metrics
duration: 5min
completed: 2026-02-25
---

# Phase 3 Plan 03: Property-Based Tests Summary

**Proptest-powered property-based tests verifying GROUP BY inference, SELECT aliases, SQL structure, join pruning, and filter composition invariants across arbitrary dimension/metric subsets**

## Performance

- **Duration:** 5 min
- **Started:** 2026-02-24T23:54:58Z
- **Completed:** 2026-02-25T00:00:51Z
- **Tasks:** 2
- **Files modified:** 2

## Accomplishments
- 6 property-based tests cover all expansion engine invariants with 256 random cases each
- GROUP BY inference verified: all requested dimensions appear in GROUP BY, absent for global aggregates
- SELECT alias verification: all requested dimension and metric names appear as aliases
- SQL structural validity: CTE pattern (WITH, SELECT, FROM) always correct
- Join pruning verified: joins only included when source_table references require them
- Filter composition verified: definition filters always present in generated SQL
- Full test suite green: 45 unit tests + 6 proptest + 1 doctest = 52 total

## Task Commits

Each task was committed atomically:

1. **Task 1: Add proptest dev-dependency and create test fixtures** - `7293da7` (feat)
2. **Task 2: Implement property-based tests** - included in `7293da7` (combined with Task 1)

_Note: Both tasks implemented in a single pass since fixtures and tests were created together in the same file_

## Files Created/Modified
- `tests/expand_proptest.rs` - 6 property-based tests with two fixture definitions and arb_query_request strategy
- `Cargo.toml` - Added proptest 1.9 dev-dependency; added "lib" to crate-type for integration test support

## Decisions Made
- Added `"lib"` to `crate-type` alongside `"cdylib"`: Rust integration tests (in `tests/`) need to link against the crate as a library; `cdylib` alone only produces a dynamic library for FFI consumers, not a linkable Rust artifact. This is a standard Rust pattern for extensions that need both loadable-extension builds and `cargo test` integration tests.
- Used `proptest::sample::subsequence` to generate valid subsets: this directly produces random subsequences of the dimension/metric name lists, guaranteeing all generated requests reference valid names.
- Default proptest config (256 cases): the combinatorial space for 3-4 dimensions and 3 metrics is small enough that 256 cases provides thorough coverage.

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 3 - Blocking] Added "lib" to crate-type for integration test compilation**
- **Found during:** Task 1
- **Issue:** Integration tests in `tests/` cannot link against a `cdylib`-only crate; `use semantic_views::expand` failed with "unresolved module"
- **Fix:** Added `"lib"` to `crate-type` array in Cargo.toml so Cargo builds both a cdylib (for DuckDB extension loading) and a rlib (for tests)
- **Files modified:** Cargo.toml
- **Verification:** `cargo test --test expand_proptest -- --list` succeeds
- **Committed in:** 7293da7 (Task 1 commit)

**2. [Rule 1 - Bug] Fixed type inference failures in proptest macro context**
- **Found during:** Task 1
- **Issue:** Rust type inference fails inside proptest! macro for closure parameters and method calls; `|st| st.eq_ignore_ascii_case()` and `filter.as_str()` produced E0282 errors
- **Fix:** Added explicit type annotations on closure parameters (`|st: &String|`) and introduced a `let f: &str = filter;` binding for filter iteration
- **Files modified:** tests/expand_proptest.rs
- **Verification:** Compilation succeeds, all tests pass
- **Committed in:** 7293da7 (Task 1 commit)

---

**Total deviations:** 2 auto-fixed (1 blocking, 1 bug)
**Impact on plan:** Both auto-fixes necessary for compilation. No scope creep.

## Issues Encountered
None beyond the auto-fixed deviations above.

## User Setup Required
None - no external service configuration required.

## Next Phase Readiness
- Phase 3 (Expansion Engine) is fully complete: core expand(), join resolution, fuzzy matching, and property-based tests
- 52 total tests (45 unit + 6 proptest + 1 doctest) all passing
- Ready for Phase 4 (Query Interface): table function returning SQL results via expand()
- Ready for Phase 5 (Hardening): cargo-fuzz targets can build on proptest strategies

## Self-Check: PASSED

- FOUND: tests/expand_proptest.rs
- FOUND: Cargo.toml (modified)
- FOUND: commit 7293da7 (Task 1+2)
- FOUND: 03-03-SUMMARY.md

---
*Phase: 03-expansion-engine*
*Completed: 2026-02-25*
