from agent.tools.builtin.file import edit, write
from agent.tools.builtin.file.diff_utils import create_unified_diff


def test_file_tools_share_one_diff_implementation():
    assert edit._create_diff is create_unified_diff
    assert write._create_diff is create_unified_diff


def test_unified_diff_contract_is_stable():
    diff = create_unified_diff("demo.txt", "old\n", "new\n")

    assert "--- a/demo.txt" in diff
    assert "+++ b/demo.txt" in diff
    assert "-old" in diff
    assert "+new" in diff
    assert create_unified_diff("demo.txt", "same", "same") == "(无变更)"