tests: add tests for sensitivity analysis (#1662)

* fix len bug for std calc.

* add sensitivity analysis tests.

* add license header

* feedback

* add docstrings.

Author: janfb

sbi/analysis/sensitivity_analysis.py

@@ -47,7 +47,9 @@ def destandardizing_net(batch_t: Tensor, min_std: float = 1e-7) -> nn.Module:
     is_valid_t, *_ = handle_invalid_x(batch_t, True)
 
     t_mean = torch.mean(batch_t[is_valid_t], dim=0)
-    if len(batch_t > 1):
+
+    # Use batch size to decide whether a reliable std can be computed.
+    if len(batch_t) > 1:
         t_std = torch.std(batch_t[is_valid_t], dim=0)
         t_std[t_std < min_std] = min_std
     else:

tests/sensitivity_analysis_test.py

@@ -0,0 +1,310 @@
+# This file is part of sbi, a toolkit for simulation-based inference. sbi is licensed
+# under the Apache License Version 2.0, see <https://www.apache.org/licenses/>
+
+# NOTE: the entire file was drafted by GPT-5 in GH Copilot, then editied by janfb.
+
+from typing import Tuple
+
+import pytest
+import torch
+from torch import Tensor, nn
+
+from sbi.analysis.sensitivity_analysis import (
+    ActiveSubspace,
+    Destandardize,
+    build_input_output_layer,
+    destandardizing_net,
+)
+
+# ------------------------
+# Fixtures and test helpers
+# ------------------------
+
+
+@pytest.fixture
+def toy_theta_property() -> Tuple[Tensor, Tensor]:
+    """Small synthetic (theta, property) dataset for regression testing."""
+    n, d = 64, 3
+    theta = torch.randn(n, d)
+    y = theta.sum(dim=1, keepdim=True) + 0.05 * torch.randn(n, 1)
+    return theta, y
+
+
+class _PriorWithStats:
+    """Simple Gaussian prior with mean and stddev attributes."""
+
+    def __init__(self, d: int):
+        self.mean = torch.zeros(d)
+        self.stddev = torch.ones(d)
+
+    def sample(self, shape: Tuple[int, ...]) -> Tensor:
+        return torch.randn(*shape, self.mean.numel())
+
+
+class _PriorWithoutStats:
+    """Simple prior without mean and stddev attributes."""
+
+    def __init__(self, d: int):
+        self._d = d
+
+    def sample(self, shape: Tuple[int, ...]) -> Tensor:
+        return torch.randn(*shape, self._d)
+
+
+class _PosteriorStub:
+    """Stub posterior with simple Gaussian prior and quadratic potential."""
+
+    def __init__(self, d: int, with_stats: bool = True):
+        self._device = "cpu"
+        self.d = d
+        self.prior = _PriorWithStats(d) if with_stats else _PriorWithoutStats(d)
+
+    def sample(self, shape: Tuple[int, ...]) -> Tensor:
+        return torch.randn(*shape, self.d, requires_grad=False)
+
+    def potential(self, theta: Tensor, track_gradients: bool = True) -> Tensor:
+        # Smooth, concave potential with gradient everywhere
+        # Return shape (N, 1) to match regression output style
+        return -(theta**2).sum(dim=1, keepdim=True) * 0.5
+
+
+@pytest.fixture(
+    params=[
+        pytest.param(True, id="prior_with_stats"),
+        pytest.param(False, id="prior_without_stats"),
+    ]
+)
+def posterior_stub(request) -> _PosteriorStub:
+    """Fixture providing a stub posterior with and without prior stats."""
+    return _PosteriorStub(d=3, with_stats=request.param)
+
+
+@pytest.fixture
+def embedding_net_theta() -> nn.Module:
+    """Small embedding net for theta."""
+    return nn.Sequential(nn.Linear(3, 3), nn.ReLU())
+
+
+# ------------------------
+# Utility layer tests
+# ------------------------
+
+
+def test_destandardize_and_destandardizing_net_forward() -> None:
+    """Tests destandardizing_net and Destandardize layer."""
+    # Create a batch with near-zero variance in one dim to exercise min-std flooring
+    n, d = 50, 2
+    col0 = torch.randn(n, 1)
+    col1 = torch.zeros(n, 1)
+    batch = torch.cat([col0, col1], dim=1)
+
+    min_std = 0.5
+    net = destandardizing_net(batch, min_std=min_std)
+    # Expected mean and clamped std
+    mean = batch.mean(dim=0)
+    std = batch.std(dim=0)
+    std = torch.where(std < min_std, torch.full_like(std, min_std), std)
+
+    # Check that zero maps to mean, ones maps to mean + std
+    out0 = net(torch.zeros(1, d))
+    out1 = net(torch.ones(1, d))
+    assert torch.allclose(out0, mean.unsqueeze(0), atol=1e-6)
+    assert torch.allclose(out1, (mean + std).unsqueeze(0), atol=1e-6)
+
+    # Also test Destandardize directly
+    dn = Destandardize(mean, std)
+    assert torch.allclose(dn(torch.zeros(1, d)), out0)
+
+
+def test_destandardizing_net_single_sample_branch() -> None:
+    """Tests destandardizing_net when batch has a single row."""
+    # When batch has a single row, we enter the else-branch and use t_std = 1
+    batch = torch.tensor([[2.0, -3.0]], dtype=torch.float32)
+    net = destandardizing_net(batch, min_std=0.5)
+    # For standardized input 0, output should equal mean (the single row)
+    out0 = net(torch.zeros(1, 2))
+    assert torch.allclose(out0, batch, atol=1e-6)
+    # For standardized input 1, output should be mean + std (std == 1 here)
+    out1 = net(torch.ones(1, 2))
+    assert torch.allclose(out1, batch + 1.0, atol=1e-6)
+
+
+@pytest.mark.parametrize(
+    "z_theta, z_prop",
+    [
+        (True, True),
+        (True, False),
+        (False, True),
+        (False, False),
+    ],
+)
+def test_build_input_output_layer_shapes_and_types(
+    toy_theta_property, embedding_net_theta, z_theta, z_prop
+) -> None:
+    """Sanity check that the built input-output layer can be composed
+
+    Args:
+        toy_theta_property: Fixture providing (theta, property) data
+        embedding_net_theta: Fixture providing a small embedding net for theta
+        z_theta: Whether to z-score standardize theta
+        z_prop: Whether to z-score standardize the property
+    """
+    theta, y = toy_theta_property
+    inp, out = build_input_output_layer(
+        batch_theta=theta,
+        batch_property=y,
+        z_score_theta=z_theta,
+        z_score_property=z_prop,
+        embedding_net_theta=embedding_net_theta,
+    )
+    # Compose a tiny regression head to ensure shape compatibility end-to-end
+    head = nn.Linear(theta.shape[1], 1)
+    model = nn.Sequential(inp, head, out)
+    preds = model(theta)
+    assert preds.shape == y.shape
+
+
+# ------------------------
+# ActiveSubspace tests
+# ------------------------
+
+
+@pytest.mark.parametrize("model_name", ["mlp", "resnet"])
+@pytest.mark.parametrize("clip_max_norm", [None, 5.0])
+def test_add_property_and_train_models(
+    model_name,
+    clip_max_norm,
+    toy_theta_property,
+    posterior_stub,
+    embedding_net_theta,
+) -> None:
+    """Tests that add_property and train run without error for different models."""
+    theta, y = toy_theta_property
+    a = ActiveSubspace(posterior_stub)
+    a.add_property(
+        theta=theta,
+        emergent_property=y,
+        model=model_name,
+        hidden_features=16,
+        num_blocks=1,
+        dropout_probability=0.1,
+        z_score_theta=True,
+        z_score_property=True,
+        embedding_net=embedding_net_theta,
+    )
+    net = a.train(
+        training_batch_size=16,
+        learning_rate=1e-3,
+        validation_fraction=0.25,
+        stop_after_epochs=2,
+        max_num_epochs=3,
+        clip_max_norm=clip_max_norm,
+    )
+    assert isinstance(net, nn.Module)
+    assert len(a._validation_log_probs) >= 1
+
+
+def test_add_property_with_callable_model(toy_theta_property, posterior_stub) -> None:
+    """Tests that add_property works with a user-defined model builder."""
+    theta, y = toy_theta_property
+
+    def builder(batch_theta: Tensor) -> nn.Module:
+        d = batch_theta.shape[1]
+        return nn.Sequential(nn.Identity(), nn.Linear(d, 1))
+
+    a = ActiveSubspace(posterior_stub)
+    a.add_property(theta=theta, emergent_property=y, model=builder)
+    net = a.train(training_batch_size=16, stop_after_epochs=1, max_num_epochs=2)
+    assert isinstance(net, nn.Module)
+
+
+def test_add_property_invalid_model_raises(toy_theta_property, posterior_stub) -> None:
+    """Tests that add_property raises for invalid model name."""
+    theta, y = toy_theta_property
+    a = ActiveSubspace(posterior_stub)
+    with pytest.raises(NameError):
+        a.add_property(theta=theta, emergent_property=y, model="unknown")
+
+
+def test_train_reuses_existing_net(toy_theta_property, posterior_stub) -> None:
+    theta, y = toy_theta_property
+    a = ActiveSubspace(posterior_stub)
+    a.add_property(theta=theta, emergent_property=y, model="mlp", hidden_features=8)
+    _ = a.train(training_batch_size=16, stop_after_epochs=1, max_num_epochs=2)
+    first_id = id(a._regression_net)
+    _ = a.train(training_batch_size=16, stop_after_epochs=1, max_num_epochs=2)
+    assert id(a._regression_net) == first_id  # net is reused, not rebuilt
+
+
+@pytest.mark.parametrize("norm_gradients", [True, False])
+def test_find_directions_with_regression_net(
+    norm_gradients, toy_theta_property, posterior_stub
+) -> None:
+    """Tests that find_directions runs and returns correctly shaped outputs."""
+    theta, y = toy_theta_property
+    a = ActiveSubspace(posterior_stub)
+    a.add_property(theta=theta, emergent_property=y, model="mlp", hidden_features=8)
+    a.train(training_batch_size=16, stop_after_epochs=1, max_num_epochs=2)
+
+    evals, evecs = a.find_directions(
+        posterior_log_prob_as_property=False,
+        norm_gradients_to_prior=norm_gradients,
+        num_monte_carlo_samples=128,
+    )
+    d = theta.shape[1]
+    assert evals.shape == (d,)
+    assert evecs.shape == (d, d)
+    # Ascending order
+    assert torch.all(evals[1:] >= evals[:-1])
+    # Columns are unit vectors
+    assert torch.allclose(torch.linalg.norm(evecs, dim=0), torch.ones(d), atol=1e-5)
+
+
+def test_find_directions_with_posterior_log_prob_warns(
+    toy_theta_property, posterior_stub
+) -> None:
+    """Tests that find_directions with posterior log-prob issues a warning."""
+    theta, y = toy_theta_property
+    a = ActiveSubspace(posterior_stub)
+    a.add_property(theta=theta, emergent_property=y, model="mlp", hidden_features=8)
+    a.train(training_batch_size=16, stop_after_epochs=1, max_num_epochs=2)
+
+    with pytest.warns(UserWarning):
+        evals, evecs = a.find_directions(
+            posterior_log_prob_as_property=True,
+            norm_gradients_to_prior=True,
+            num_monte_carlo_samples=64,
+        )
+    assert evals.numel() == evecs.shape[0]
+
+
+def test_find_directions_raises_without_property(posterior_stub) -> None:
+    """Tests that find_directions raises if no property was added."""
+    a = ActiveSubspace(posterior_stub)
+    with pytest.raises(ValueError):
+        _ = a.find_directions(
+            posterior_log_prob_as_property=False, num_monte_carlo_samples=8
+        )
+
+
+@pytest.mark.parametrize("norm_gradients", [True, False])
+def test_project_after_find_directions(
+    norm_gradients, toy_theta_property, posterior_stub
+) -> None:
+    """Tests that project works after find_directions and returns correct shapes."""
+    theta, y = toy_theta_property
+    a = ActiveSubspace(posterior_stub)
+    a.add_property(theta=theta, emergent_property=y, model="mlp", hidden_features=8)
+    a.train(training_batch_size=16, stop_after_epochs=1, max_num_epochs=2)
+    _evals, _evecs = a.find_directions(
+        posterior_log_prob_as_property=False,
+        norm_gradients_to_prior=norm_gradients,
+        num_monte_carlo_samples=64,
+    )
+
+    proj1 = a.project(theta, num_dimensions=1)
+    proj2 = a.project(theta, num_dimensions=2)
+    assert proj1.shape == (theta.shape[0], 1)
+    assert proj2.shape == (theta.shape[0], 2)
+    # Different dimensionality gives different projections
+    assert not torch.allclose(proj1, proj2[:, :1])