Fix Python RePL Tool (#4137)

Filter out kwargs from inferred schema when determining if a tool is
single input.

Add a couple unit tests.

Move tool unit tests to the tools dir

tests/unit_tests/tools/python/test_python.py

@@ -0,0 +1,23 @@
+"""Test Python REPL Tools."""
+import sys
+
+import pytest
+
+from langchain.tools.python.tool import PythonAstREPLTool, PythonREPLTool
+
+
+def test_python_repl_tool_single_input() -> None:
+    """Test that the python REPL tool works with a single input."""
+    tool = PythonREPLTool()
+    assert tool.is_single_input
+    assert int(tool.run("print(1 + 1)").strip()) == 2
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 9), reason="Requires python version >= 3.9 to run."
+)
+def test_python_ast_repl_tool_single_input() -> None:
+    """Test that the python REPL tool works with a single input."""
+    tool = PythonAstREPLTool()
+    assert tool.is_single_input
+    assert tool.run("1 + 1") == 2