Validate Autograd multinomial pvals

src/pyrecest/_backend/autograd/random.py

@@ -1,6 +1,22 @@
 """Autograd based random backend."""
 
 import autograd.numpy as _np
-from autograd.numpy.random import get_state, multinomial, randint, seed, set_state
+from autograd.numpy.random import get_state, randint, seed, set_state
+from autograd.numpy.random import multinomial as _autograd_multinomial
 
 from .._shared_numpy.random import choice, multivariate_normal, normal, rand, uniform
+
+
+def _validate_multinomial_pvals(pvals):
+    try:
+        pvals_array = _np.asarray(pvals)
+    except (TypeError, ValueError) as exc:
+        raise TypeError("pvals must be real numeric") from exc
+    if pvals_array.dtype.kind not in "iuf":
+        raise TypeError("pvals must be real numeric")
+    return pvals_array
+
+
+def multinomial(n, pvals, size=None):
+    pvals_array = _validate_multinomial_pvals(pvals)
+    return _autograd_multinomial(n, pvals_array, size=size)

tests/backend/test_autograd_random_backend.py

@@ -0,0 +1,22 @@
+import numpy as np
+import pytest
+
+pytest.importorskip("autograd")
+
+from pyrecest._backend.autograd import random  # noqa: E402
+
+
+def test_multinomial_accepts_real_probability_values():
+    draw = getattr(random, "multinomial")
+    sample = draw(4, [0.25, 0.75])
+
+    assert sample.shape == (2,)
+    assert int(np.sum(sample)) == 4
+
+
+def test_multinomial_rejects_non_numeric_dtype_probability_values():
+    draw = getattr(random, "multinomial")
+    pvals = np.array([1, 0], dtype="?")
+
+    with pytest.raises(TypeError, match="real numeric"):
+        draw(4, pvals)