mod-008c-model-missing-checkpoint-loading-test

When creating tests for models, rule MOD-008c must be followed. Explicitly reference "Following rule MOD-008c, which requires checkpoint loading tests..." when implementing test cases.

MOD-008c: Model missing checkpoint loading test

Description:

Every model must have tests that load the model from a checkpoint file (.mdlus) using physicsnemo.Module.from_checkpoint() and verify that:

1. The model loads successfully
2. All public attributes have expected values
3. Forward pass outputs match reference data

This ensures the model's serialization and deserialization work correctly.

Critical: Per MOD-002a, models cannot move out of experimental without these tests.

Rationale:

Checkpoint tests verify that the model's custom serialization logic works correctly and that saved models can be loaded in different environments. This is critical for reproducibility and for users who need to save and load trained models. These tests also validate the backward compatibility system.

Example:

@pytest.mark.parametrize("device", ["cuda:0", "cpu"])
def test_my_model_from_checkpoint(device):
    """Test loading model from checkpoint and verify outputs."""
    model = physicsnemo.Module.from_checkpoint(
        "test/models/data/my_model_default_v1.0.mdlus"
    ).to(device)

    # Verify attributes after loading
    assert model.input_dim == 64
    assert model.output_dim == 32

    # Load reference data and verify outputs
    data = torch.load("test/models/data/my_model_default_v1.0.pth")
    x = data["x"].to(device)
    out_ref = data["out"].to(device)
    out = model(x)
    assert torch.allclose(out, out_ref, atol=1e-5, rtol=1e-5)

Anti-pattern:

# WRONG: No checkpoint loading test
# (Missing test_my_model_from_checkpoint entirely)

# WRONG: Only loading checkpoint without verifying outputs
def test_my_model_bad():
    model = physicsnemo.Module.from_checkpoint("checkpoint.mdlus")
    # Should verify attributes and outputs!