test(stress): add ignored stress tests for large-scale scenarios

- 10k sequential trials with RandomSampler
- 128 parameters with TPE sampler
- 128 concurrent workers with optimize_parallel
- 5k trials with TPE and 32 parallel workers

tests/stress_tests.rs

@@ -0,0 +1,129 @@
+//! Stress and large-scale tests for the optimizer library.
+//!
+//! All tests are `#[ignore]`-gated so they don't run in normal CI.
+//! Run with: `cargo test --features async -- --ignored`
+
+use std::collections::HashSet;
+
+use optimizer::parameter::{FloatParam, Parameter};
+use optimizer::sampler::random::RandomSampler;
+use optimizer::sampler::tpe::TpeSampler;
+use optimizer::{Direction, Error, Study};
+
+fn make_float_params(n: usize) -> Vec<FloatParam> {
+    (0..n)
+        .map(|i| FloatParam::new(-5.0, 5.0).name(format!("x{i}")))
+        .collect()
+}
+
+fn sphere(trial: &mut optimizer::Trial, params: &[FloatParam]) -> Result<f64, Error> {
+    let mut sum = 0.0;
+    for p in params {
+        let v = p.suggest(trial)?;
+        sum += v * v;
+    }
+    Ok(sum)
+}
+
+#[test]
+#[ignore]
+fn stress_many_trials_random() {
+    let sampler = RandomSampler::with_seed(42);
+    let study: Study<f64> = Study::with_sampler(Direction::Minimize, sampler);
+    let params = make_float_params(5);
+
+    study
+        .optimize(10_000, |trial: &mut optimizer::Trial| {
+            sphere(trial, &params)
+        })
+        .expect("10k trials should complete");
+
+    assert_eq!(study.n_trials(), 10_000);
+    let best = study.best_value().expect("should have a best value");
+    assert!(best.is_finite(), "best value should be finite");
+    assert!(best >= 0.0, "sphere function is non-negative");
+}
+
+#[test]
+#[ignore]
+fn stress_many_params_tpe() {
+    let sampler = TpeSampler::builder()
+        .seed(42)
+        .n_startup_trials(10)
+        .build()
+        .unwrap();
+    let study: Study<f64> = Study::with_sampler(Direction::Minimize, sampler);
+    let params = make_float_params(128);
+
+    study
+        .optimize(200, |trial: &mut optimizer::Trial| sphere(trial, &params))
+        .expect("200 trials with 128 params should complete");
+
+    assert_eq!(study.n_trials(), 200);
+
+    let best = study.best_trial().expect("should have a best trial");
+    assert_eq!(best.params.len(), 128, "best trial should have 128 params");
+    assert!(best.value.is_finite(), "best value should be finite");
+    for v in best.params.values() {
+        let f = match v {
+            optimizer::param::ParamValue::Float(f) => *f,
+            other => panic!("expected Float param, got {other}"),
+        };
+        assert!(f.is_finite(), "all param values should be finite");
+    }
+}
+
+#[cfg(feature = "async")]
+#[tokio::test]
+#[ignore]
+async fn stress_high_concurrency_parallel() {
+    let sampler = RandomSampler::with_seed(42);
+    let study: Study<f64> = Study::with_sampler(Direction::Minimize, sampler);
+    let params = make_float_params(10);
+
+    study
+        .optimize_parallel(1_000, 128, move |trial: &mut optimizer::Trial| {
+            sphere(trial, &params)
+        })
+        .await
+        .expect("1k trials with 128 workers should complete");
+
+    assert_eq!(study.n_trials(), 1_000);
+
+    let trials = study.trials();
+    let ids: HashSet<u64> = trials.iter().map(|t| t.id).collect();
+    assert_eq!(ids.len(), 1_000, "all trial IDs should be unique");
+
+    let best = study.best_value().expect("should have a best value");
+    assert!(best.is_finite(), "best value should be finite");
+}
+
+#[cfg(feature = "async")]
+#[tokio::test]
+#[ignore]
+async fn stress_long_running_tpe_parallel() {
+    let sampler = TpeSampler::builder()
+        .seed(42)
+        .n_startup_trials(20)
+        .build()
+        .unwrap();
+    let study: Study<f64> = Study::with_sampler(Direction::Minimize, sampler);
+    let params = make_float_params(20);
+
+    study
+        .optimize_parallel(5_000, 32, move |trial: &mut optimizer::Trial| {
+            sphere(trial, &params)
+        })
+        .await
+        .expect("5k trials with TPE and 32 workers should complete");
+
+    assert_eq!(study.n_trials(), 5_000);
+
+    let trials = study.trials();
+    let ids: HashSet<u64> = trials.iter().map(|t| t.id).collect();
+    assert_eq!(ids.len(), 5_000, "all trial IDs should be unique");
+
+    let best = study.best_trial().expect("should have a best trial");
+    assert!(best.value.is_finite(), "best value should be finite");
+    assert_eq!(best.params.len(), 20, "best trial should have 20 params");
+}