PyTensor integration tests are always skipped

[williambdean]

Summary

The PyTensor integration tests in test_helpers.py are unconditionally skipped with skipif(True, ...), meaning they never run even when PyTensor is installed. Given that PyTensor compatibility was a key design goal (mentioned in the helpers module docstring), these tests should run when PyTensor is available.

Current Behavior

@pytest.mark.skipif(True, reason="PyTensor not required for core functionality")
class TestPyTensorOps:
    """Test PyTensor operations (skipped if PyTensor not available)."""
    
    def test_pytensor_ops_lazy_import(self):
        # This NEVER runs
        ...

Expected Behavior

Tests should be conditionally skipped based on PyTensor availability:

pytensor_available = False
try:
    import pytensor
    pytensor_available = True
except ImportError:
    pass

@pytest.mark.skipif(not pytensor_available, reason="PyTensor not installed")
class TestPyTensorOps:
    """Test PyTensor operations."""
    
    def test_pytensor_ops_work_with_helpers(self):
        import pytensor.tensor as pt
        from conjugate.helpers import poisson_gamma_inputs, pytensor_ops
        
        # Test that pytensor_ops can be used with helpers
        data = pt.as_tensor_variable([1, 2, 3, 4, 5])
        inputs = poisson_gamma_inputs(data, **pytensor_ops)
        # Verify the result is a PyTensor expression
        ...

Why This Matters

1. PyTensor integration is a key feature - The helpers module docstring specifically mentions PyTensor compatibility:

   """For PyTensor compatibility:
       from conjugate.helpers import poisson_gamma_inputs, pytensor_ops
       inputs = poisson_gamma_inputs(observations, **pytensor_ops)
   """

2. The feedback document highlights this - PyMC integration (which uses PyTensor) was the primary motivation for creating the helpers module.

3. Untested code paths - Without tests, regressions in PyTensor support could go unnoticed.

Suggested Fix

import pytest

try:
    import pytensor
    import pytensor.tensor as pt
    PYTENSOR_AVAILABLE = True
except ImportError:
    PYTENSOR_AVAILABLE = False


@pytest.mark.skipif(not PYTENSOR_AVAILABLE, reason="PyTensor not installed")
class TestPyTensorOps:
    """Test PyTensor operations when PyTensor is available."""

    def test_pytensor_ops_contains_expected_keys(self):
        from conjugate.helpers import pytensor_ops
        
        assert "sum_fn" in pytensor_ops
        assert "len_fn" in pytensor_ops
        assert "prod_fn" in pytensor_ops
        assert callable(pytensor_ops["sum_fn"])

    def test_pytensor_ops_with_poisson_gamma(self):
        from conjugate.helpers import poisson_gamma_inputs, pytensor_ops
        
        data = pt.as_tensor_variable([1.0, 2.0, 3.0, 4.0, 5.0])
        relevant_ops = {k: v for k, v in pytensor_ops.items() if k in ["sum_fn", "len_fn"]}
        result = poisson_gamma_inputs(data, **relevant_ops)
        
        # Compile and evaluate
        import pytensor
        x_total_fn = pytensor.function([], result["x_total"])
        n_fn = pytensor.function([], result["n"])
        
        assert x_total_fn() == 15.0
        assert n_fn() == 5

Optional: CI Integration

Consider adding a CI job that installs PyTensor and runs these tests:

# In .github/workflows/tests.yml
jobs:
  test-pytensor:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Install with PyTensor
        run: |
          pip install pytensor
          pip install -e .
      - name: Run PyTensor tests
        run: pytest tests/test_helpers.py -k "PyTensor" -v