add simple cross-invocation hash stability test

test/test_pytato.py

@@ -1144,8 +1144,47 @@ def test_get_hash():
         seen_hashes.add(h1)
 
 
+def run_test_with_hashseed(f, *args):
+    from pickle import dumps
+    from base64 import b64encode
+
+    from subprocess import check_call
+    import os
+
+    os.environ["RUN_WITH_SET_PYTHONHASHSEED"] = "1"
+    os.environ["PYTHONHASHSEED"] = "1"
+    os.environ["INVOCATION_INFO"] = b64encode(dumps((f, args))).decode()
+
+    check_call([sys.executable, __file__])
+
+
+def run_test_with_hashseed_inner():
+    from pickle import loads
+    from base64 import b64decode
+    f, args = loads(b64decode(os.environ["INVOCATION_INFO"].encode()))
+
+    f(*args)
+
+
+def test_get_hash_stable_with_hashseed():
+    run_test_with_hashseed(_do_test_get_hash_stable_with_hashseed)
+
+
+def _do_test_get_hash_stable_with_hashseed():
+    rdagc = RandomDAGContext(np.random.default_rng(seed=42),
+                axis_len=5, use_numpy=False)
+
+    dag = make_random_dag(rdagc)
+    assert hash(dag) == 6313690382525417492
+
+# }}}
+
+
 if __name__ == "__main__":
-    if len(sys.argv) > 1:
+    import os
+    if "RUN_WITH_SET_PYTHONHASHSEED" in os.environ:
+        run_test_with_hashseed_inner()
+    elif len(sys.argv) > 1:
         exec(sys.argv[1])
     else:
         from pytest import main