Reproduce #967 in a test

tests/test_pre_commit_1_sync_with_no_config.py

@@ -0,0 +1,95 @@
+from copy import deepcopy
+
+import pytest
+from git.exc import HookExecutionError
+from nbformat.v4.nbbase import new_markdown_cell
+from pre_commit.main import main as pre_commit
+
+import jupytext
+from jupytext import TextFileContentsManager
+from jupytext.compare import compare_notebooks
+
+from .utils import (
+    skip_pre_commit_tests_on_windows,
+    skip_pre_commit_tests_when_jupytext_folder_is_not_a_git_repo,
+)
+
+
+@skip_pre_commit_tests_on_windows
+@skip_pre_commit_tests_when_jupytext_folder_is_not_a_git_repo
+def test_pre_commit_hook_sync_with_no_config(
+    tmpdir,
+    cwd_tmpdir,
+    tmp_repo,
+    jupytext_repo_root,
+    jupytext_repo_rev,
+    notebook_with_outputs,
+):
+    """In this test we reproduce the setting from https://github.com/mwouts/jupytext/issues/967"""
+    pre_commit_config_yaml = f"""
+repos:
+- repo: {jupytext_repo_root}
+  rev: {jupytext_repo_rev}
+  hooks:
+  - id: jupytext
+    args: [
+      '--sync',
+      '--set-formats',
+      'ipynb,py:percent',
+      '--show-changes',
+      '--'
+    ]
+    files: ^notebooks/
+"""
+    # Save a sample notebook with outputs in Jupyter
+    nb = deepcopy(notebook_with_outputs)
+    (tmpdir / "notebooks").mkdir()
+    cm = TextFileContentsManager()
+    cm.root_dir = str(tmpdir)
+    cm.save(dict(type="notebook", content=nb), "notebooks/nb.ipynb")
+
+    # Add it to git
+    tmp_repo.git.add("notebooks/nb.ipynb")
+    tmp_repo.index.commit("Notebook with outputs")
+
+    # Configure the pre-commit hook
+    tmpdir.join(".pre-commit-config.yaml").write(pre_commit_config_yaml)
+    tmp_repo.git.add(".pre-commit-config.yaml")
+    pre_commit(["install", "--install-hooks", "-f"])
+
+    # Modify and save the notebook
+    nb.cells.append(new_markdown_cell("New markdown cell"))
+    cm.save(dict(type="notebook", content=nb), "notebooks/nb.ipynb")
+
+    # No .py file at the moment
+    assert not (tmpdir / "notebooks" / "nb.py").exists()
+
+    # try to commit it, should fail as the py version hasn't been added
+    tmp_repo.git.add("notebooks/nb.ipynb")
+    with pytest.raises(
+        HookExecutionError,
+        match="git add notebooks/nb.py",
+    ):
+        tmp_repo.index.commit("failing")
+
+    # Now the .py file is present
+    assert "New markdown cell" in tmpdir.join("notebooks/nb.py").read()
+
+    # add the ipynb and the py file, now the commit will succeed
+    tmp_repo.git.add("notebooks/nb.ipynb")
+    tmp_repo.git.add("notebooks/nb.py")
+    tmp_repo.index.commit("passing")
+    assert "notebooks/nb.ipynb" in tmp_repo.tree()
+    assert "notebooks/nb.py" in tmp_repo.tree()
+
+    # The notebook on disk is the same as the original, except for the new cell added
+    nb = jupytext.read(tmpdir / "notebooks" / "nb.ipynb")
+    extra_cell = nb.cells.pop()
+    assert extra_cell.cell_type == "markdown"
+    assert extra_cell.source == "New markdown cell"
+    compare_notebooks(
+        nb,
+        notebook_with_outputs,
+        compare_ids=True,
+        compare_outputs=True,
+    )