BashChain (#260)

Love the project, a ton of fun!

I think the PR is pretty self-explanatory, happy to make any changes! I
am working on using it in an `LLMBashChain` and may update as that
progresses.

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

tests/unit_tests/chains/test_bash.py

@@ -0,0 +1,44 @@
+import subprocess
+from pathlib import Path
+
+from langchain.utilities.bash import BashProcess
+
+def test_pwd_command() -> None:
+    """Test correct functionality."""
+    session = BashProcess()
+    commands = ["pwd"]
+    output = session.run(commands)
+    print(output)
+
+    assert output["outputs"] == [subprocess.check_output("pwd", shell=True).decode()]
+
+def test_incorrect_command() -> None:
+    """Test handling of incorrect command."""
+    session = BashProcess()
+    output = session.run(["invalid_command"])
+    assert output["success"] is False
+
+def test_create_directory_and_files(tmp_path: Path) -> None:
+    """Test creation of a directory and files in a temporary directory."""
+    session = BashProcess(strip_newlines=True)
+
+    # create a subdirectory in the temporary directory
+    temp_dir = tmp_path / "test_dir"
+    temp_dir.mkdir()
+
+    # run the commands in the temporary directory
+    commands = [
+        f"touch {temp_dir}/file1.txt",
+        f"touch {temp_dir}/file2.txt",
+        f"echo 'hello world' > {temp_dir}/file2.txt",
+        f"cat {temp_dir}/file2.txt"
+    ]
+
+    output = session.run(commands)
+    assert output["success"] is True
+    assert output["outputs"][-1] == "hello world"
+
+    # check that the files were created in the temporary directory
+    output = session.run([f"ls {temp_dir}"])
+    assert output["success"] is True
+    assert output["outputs"] == ["file1.txt\nfile2.txt"]

tests/unit_tests/chains/test_llm_bash.py

@@ -0,0 +1,24 @@
+"""Test LLM Bash functionality."""
+
+import pytest
+
+from langchain.chains.llm_bash.base import LLMBashChain
+from langchain.chains.llm_bash.prompt import _PROMPT_TEMPLATE
+from tests.unit_tests.llms.fake_llm import FakeLLM
+
+
+@pytest.fixture
+def fake_llm_bash_chain() -> LLMBashChain:
+    """Fake LLM Bash chain for testing."""
+    queries = {
+        _PROMPT_TEMPLATE.format(question="Please write a bash script that prints 'Hello World' to the console."): "```bash\nexpr 1 + 1\n```",
+    }
+    fake_llm = FakeLLM(queries=queries)
+    return LLMBashChain(llm=fake_llm, input_key="q", output_key="a")
+
+
+def test_simple_question(fake_llm_bash_chain: LLMBashChain) -> None:
+    """Test simple question that should not need python."""
+    question = "Please write a bash script that prints 'Hello World' to the console."
+    output = fake_llm_bash_chain.run(question)
+    assert output == {'commands': ['expr 1 + 1'], 'output': {'outputs': ['2\n'], 'success': True}}