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//! Unit tests for `AdaptivePI<C>` (v0.6.0, ADR-0014).
//!
//! Six tests:
//! 1. `default_construction` — defaults match ADR-0014 for τ-order-2 inner (post-D1, math.md §11.1.bis).
//! 2. `with_tolerance_builder` — builder overrides `tol_abs` and `tol_rel`.
//! 3. `accepts_loose_tol` — at tol_rel=1e-2, smooth heat: few steps, no rejects.
//! 4. `accepts_strict_tol` — at tol_rel=1e-8 (post-D1 p=2), smooth heat: many steps taken.
//! 5. `runaway_protection` — `max_substeps=5` with impossibly tight tol triggers
//! `AdaptiveStepRejected`.
//! 6. `last_tau_is_finite` — `outcome.last_tau` is always finite after clean run.
use semiflow::{
boundary::InterpKind, AdaptivePI, BoundaryPolicy, Diffusion4thChernoff, DiffusionChernoff,
Grid1D, GridFn1D, SemiflowError,
};
// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------
fn heat_grid(n: usize) -> Grid1D {
// Explicitly pin to CubicHermite: these AdaptivePI unit tests are calibrated
// against the v1.0.0 step-count baselines (e.g. ≥200 steps for strict tol).
// v6.0 changed Grid1D::new default to SepticHermite (ADR-0109), which reduces
// spatial error and allows larger time-steps — but the step-count gates would
// then need re-calibration. Pin CubicHermite so the AdaptivePI logic is tested
// independently of the spatial kernel change.
Grid1D::new(-10.0, 10.0, n)
.unwrap()
.with_boundary(BoundaryPolicy::Reflect)
.with_interp(InterpKind::CubicHermite)
}
fn gaussian_ic(grid: Grid1D) -> GridFn1D {
GridFn1D::from_fn(grid, |x| libm::exp(-x * x / 2.0))
}
fn d4_const(grid: Grid1D) -> Diffusion4thChernoff {
Diffusion4thChernoff::new(|_| 0.5, |_| 0.0, |_| 0.0, 0.5, grid)
}
fn d2_const(grid: Grid1D) -> DiffusionChernoff {
DiffusionChernoff::new(|_| 0.5, |_| 0.0, |_| 0.0, 0.5, grid)
}
// ---------------------------------------------------------------------------
// Test 1: default construction
// ---------------------------------------------------------------------------
#[test]
fn default_construction() {
let grid = heat_grid(100);
let d4 = d4_const(grid);
let pi = AdaptivePI::new(d4);
// τ-order-2 inner (post-D1, math.md §11.1.bis): alpha = 0.7/2 = 0.35, beta = 0.4/2 = 0.2
let expected_alpha = 0.7 / 2.0;
let expected_beta = 0.4 / 2.0;
assert!(
(pi.alpha() - expected_alpha).abs() < 1e-15,
"alpha = {} != 0.35",
pi.alpha()
);
assert!(
(pi.beta() - expected_beta).abs() < 1e-15,
"beta = {} != 0.2",
pi.beta()
);
assert!((pi.safety - 0.9).abs() < 1e-15);
assert!((pi.min_ratio - 0.2).abs() < 1e-15);
assert!((pi.max_ratio - 5.0).abs() < 1e-15);
assert_eq!(pi.max_substeps, 100_000);
assert!((pi.tol_abs - 1e-8).abs() < 1e-20);
assert!((pi.tol_rel - 1e-6).abs() < 1e-18);
}
// ---------------------------------------------------------------------------
// Test 2: with_tolerance builder
// ---------------------------------------------------------------------------
#[test]
fn with_tolerance_builder() {
let grid = heat_grid(100);
let d4 = d4_const(grid);
let pi = AdaptivePI::new(d4).with_tolerance(1e-10, 1e-8);
assert!((pi.tol_abs - 1e-10).abs() < 1e-22, "tol_abs not overridden");
assert!((pi.tol_rel - 1e-8).abs() < 1e-20, "tol_rel not overridden");
// Safety and gains unchanged.
assert!((pi.safety - 0.9).abs() < 1e-15);
let _ = pi.alpha(); // smoke: accessor compiles
}
// ---------------------------------------------------------------------------
// Test 3: accepts_loose_tol
// ---------------------------------------------------------------------------
#[test]
fn accepts_loose_tol() {
let grid = heat_grid(400);
let d4 = d4_const(grid);
let mut pi = AdaptivePI::new(d4).with_tolerance(0.0, 1e-2);
let u0 = gaussian_ic(grid);
let outcome = pi
.evolve_adaptive(1.0, &u0)
.expect("should not error at loose tol");
assert!(
outcome.steps_accepted <= 30,
"loose tol: expected ≤30 accepted steps, got {}",
outcome.steps_accepted
);
assert_eq!(
outcome.steps_rejected, 0,
"loose tol: expected 0 rejected steps"
);
}
// ---------------------------------------------------------------------------
// Test 4: accepts_strict_tol
// ---------------------------------------------------------------------------
#[test]
fn accepts_strict_tol() {
// tol_rel=1e-10 was too tight for p=2 (divisor=3) within max_substeps=100k.
// Post-D1: Diffusion4thChernoff reports τ-order 2; Richardson divisor is 3
// (not 15 as with the old buggy p=4). Use tol_rel=1e-8 — still "strict"
// (forces ≥200 accepted steps) but achievable in <100k steps. See math.md §11.1.bis.
let grid = heat_grid(400);
let d4 = d4_const(grid);
let mut pi = AdaptivePI::new(d4).with_tolerance(0.0, 1e-8);
let u0 = gaussian_ic(grid);
let outcome = pi
.evolve_adaptive(1.0, &u0)
.expect("should not error at strict tol");
assert!(
outcome.steps_accepted >= 200,
"strict tol: expected ≥200 accepted steps, got {}",
outcome.steps_accepted
);
}
// ---------------------------------------------------------------------------
// Test 5: runaway_protection
// ---------------------------------------------------------------------------
#[test]
fn runaway_protection() {
let grid = heat_grid(200);
let d2 = d2_const(grid);
let mut pi = AdaptivePI::new(d2).with_tolerance(0.0, 1e-12);
pi.max_substeps = 5;
let u0 = gaussian_ic(grid);
let err = pi
.evolve_adaptive(1.0, &u0)
.expect_err("should hit runaway cap");
match err {
SemiflowError::AdaptiveStepRejected {
steps_attempted,
last_tau,
last_err,
} => {
assert_eq!(
steps_attempted, 5,
"steps_attempted should equal max_substeps=5, got {steps_attempted}"
);
assert!(last_tau.is_finite(), "last_tau must be finite: {last_tau}");
assert!(last_err.is_finite(), "last_err must be finite: {last_err}");
}
other => panic!("expected AdaptiveStepRejected, got: {other}"),
}
}
// ---------------------------------------------------------------------------
// Test 6: last_tau_is_finite
// ---------------------------------------------------------------------------
#[test]
fn last_tau_is_finite() {
let grid = heat_grid(300);
let d4 = d4_const(grid);
let mut pi = AdaptivePI::new(d4).with_tolerance(0.0, 1e-4);
let u0 = gaussian_ic(grid);
let outcome = pi.evolve_adaptive(1.0, &u0).expect("clean run");
assert!(
outcome.last_tau.is_finite() && outcome.last_tau > 0.0,
"last_tau must be finite and positive: {}",
outcome.last_tau
);
// last_tau should be within [min_ratio * initial_guess, max_ratio * initial_guess]
// times a few PI controller iterations — just verify it's in a sane range.
assert!(
outcome.last_tau < 2.0,
"last_tau unexpectedly large: {}",
outcome.last_tau
);
}