Add unit tests to binary_tree_path_sum.py (#11833)

* test: Add unit tests

* test: Add successful tests in binaree_tree_path_sum

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* Update binary_tree_path_sum.py

* Update binary_tree_path_sum.py

* Update binary_tree_path_sum.py

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>

Author: 3 people

data_structures/binary_tree/binary_tree_path_sum.py

@@ -50,6 +50,26 @@ class BinaryTreePathSum:
     >>> tree.right.right = Node(10)
     >>> BinaryTreePathSum().path_sum(tree, 8)
     2
+    >>> BinaryTreePathSum().path_sum(None, 0)
+    0
+    >>> BinaryTreePathSum().path_sum(tree, 0)
+    0
+
+    The second tree looks like this
+          0
+         / \
+        5   5
+
+    >>> tree2 = Node(0)
+    >>> tree2.left = Node(5)
+    >>> tree2.right = Node(5)
+
+    >>> BinaryTreePathSum().path_sum(tree2, 5)
+    4
+    >>> BinaryTreePathSum().path_sum(tree2, -1)
+    0
+    >>> BinaryTreePathSum().path_sum(tree2, 0)
+    1
     """
 
     target: int