Add an xfail for a currently unsupported log-probability derivation

Author: brandonwillard

tests/test_transforms.py

@@ -763,3 +763,26 @@ def test_transform_measurable_sub():
 
     with pytest.raises(DensityNotFound):
         joint_logprob(Z_rv, X_rv)
+
+
+@pytest.mark.xfail(
+    reason="Reuse of measurable variables not supported", raises=DensityNotFound
+)
+def test_transform_reused_measurable():
+
+    srng = at.random.RandomStream(0)
+
+    X_rv = srng.normal(0, 1, name="X")
+    Z_tr = at.exp(X_rv)
+
+    z_vv = at.dscalar(name="z_vv")
+
+    logprob, vvs = joint_logprob(realized={Z_tr: z_vv, X_rv: z_vv})
+
+    logp_fn = aesara.function([z_vv], logprob)
+
+    z_val = 0.1
+
+    exp_res = sp.stats.lognorm(s=1).logpdf(z_val) + sp.stats.norm().logpdf(z_val)
+
+    np.testing.assert_allclose(logp_fn(z_val), exp_res)