fix off-by-one error and add test

Author: majosm

pytato/analysis/__init__.py

@@ -560,8 +560,9 @@ class NodeMaxDepthMapper(CachedWalkMapper):
 
     def __init__(self) -> None:
         super().__init__()
-        self.depth = 0
-        self.max_depth = 0
+        # Want the first rec() call to increment to 0, so start at -1
+        self.depth = -1
+        self.max_depth = -1
 
     # FIXME: Do I need this?
     # type-ignore-reason: dropped the extra `*args, **kwargs`.

test/test_pytato.py

@@ -765,6 +765,16 @@ def test_large_dag_with_duplicates_count():
         dag, count_duplicates=False)
 
 
+def test_nodemaxdepthmapper():
+    from pytato.analysis import get_max_node_depth
+
+    x = pt.make_placeholder("x", shape=(10, 4), dtype=np.float64)
+    for i in range(9):
+        x = x + 1
+
+    assert get_max_node_depth(x) == 10
+
+
 def test_rec_get_user_nodes():
     x1 = pt.make_placeholder("x1", shape=(10, 4))
     x2 = pt.make_placeholder("x2", shape=(10, 4))