Add test for interactions between missing, default and explicit updat…

…es in `compile_pymc`

pymc/tests/test_aesaraf.py

@@ -604,3 +604,26 @@ def test_compile_pymc_with_updates():
     f = compile_pymc([], x, updates={x: x + 1})
     assert f() == 0
     assert f() == 1
+
+
+def test_compile_pymc_missing_default_explicit_updates():
+    rng = aesara.shared(np.random.default_rng(0))
+    x = pm.Normal.dist(rng=rng)
+
+    # By default, compile_pymc should update the rng of x
+    f = compile_pymc([], x)
+    assert f() != f()
+
+    # An explicit update should override the default_update, like aesara.function does
+    # For testing purposes, we use an update that leaves the rng unchanged
+    f = compile_pymc([], x, updates={rng: rng})
+    assert f() == f()
+
+    # If we specify a custom default_update directly it should use that instead.
+    rng.default_update = rng
+    f = compile_pymc([], x)
+    assert f() == f()
+
+    # And again, it should be overridden by an explicit update
+    f = compile_pymc([], x, updates={rng: x.owner.outputs[0]})
+    assert f() != f()