From 268398741898a01498b7cab46e34513c26b7238c Mon Sep 17 00:00:00 2001
From: Henry Schreiner <henryfs@princeton.edu>
Date: Mon, 15 Jun 2026 19:13:36 -0400
Subject: [PATCH 1/2] test: cover CLI paths and string-length boundary; clarify
 cls comment

- Add tests for run_on_file (reporting, max_string_length, SyntaxError
  branch) and main(), which were previously untested.
- Add a max_string_length boundary test (len == max is flagged).
- Use a fixture to restore the class-level option these tests mutate.
- Fix the misleading "# unused" comment on Flake8ASTErrorInfo.cls; it is
  the 4th tuple element flake8 expects.

Refs #86

Assisted-by: ClaudeCode:claude-opus-4.8
---
 src/flake8_errmsg/__init__.py |  2 +-
 tests/test_package.py         | 71 +++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 1 deletion(-)

diff --git a/src/flake8_errmsg/__init__.py b/src/flake8_errmsg/__init__.py
index d07090a..478e9c6 100644
--- a/src/flake8_errmsg/__init__.py
+++ b/src/flake8_errmsg/__init__.py
@@ -32,7 +32,7 @@ class Flake8ASTErrorInfo(NamedTuple):
     line_number: int
     offset: int
     msg: str
-    cls: type  # unused
+    cls: type  # the checker class; the 4th tuple element flake8 expects
 
 
 class Visitor(ast.NodeVisitor):
diff --git a/tests/test_package.py b/tests/test_package.py
index aad6b81..347c788 100644
--- a/tests/test_package.py
+++ b/tests/test_package.py
@@ -1,6 +1,9 @@
 from __future__ import annotations
 
 import ast
+import sys
+
+import pytest
 
 import flake8_errmsg as m
 
@@ -184,3 +187,71 @@ def test_err10_namedexpr_in_lambda_ok():
     results = list(m.ErrMsgASTPlugin(node).run())
     # The walrus binds in the lambda's own scope, not the raise's, so no EM106.
     assert results == []
+
+
+# --- max_string_length boundary ---
+
+
+@pytest.fixture
+def _reset_max_string_length():
+    """Restore the class-level option, which several tests mutate in place."""
+    original = m.ErrMsgASTPlugin.max_string_length
+    yield
+    m.ErrMsgASTPlugin.max_string_length = original
+
+
+@pytest.mark.usefixtures("_reset_max_string_length")
+def test_string_length_boundary():
+    node = ast.parse('raise RuntimeError("12345")\n')  # length 5
+
+    m.ErrMsgASTPlugin.max_string_length = 5  # len == max is still flagged (>=)
+    assert len(list(m.ErrMsgASTPlugin(node).run())) == 1
+
+    m.ErrMsgASTPlugin.max_string_length = 6  # len < max is ignored
+    assert list(m.ErrMsgASTPlugin(node).run()) == []
+
+
+# --- CLI / run_on_file ---
+
+
+@pytest.mark.usefixtures("_reset_max_string_length")
+def test_run_on_file_reports_errors(tmp_path, capsys):
+    path = tmp_path / "example.py"
+    path.write_text('raise RuntimeError("a long message")\n', encoding="utf-8")
+
+    m.run_on_file(str(path))
+
+    out = capsys.readouterr().out
+    assert f"{path}:1:0 EM101" in out
+
+
+@pytest.mark.usefixtures("_reset_max_string_length")
+def test_run_on_file_respects_max_string_length(tmp_path, capsys):
+    path = tmp_path / "example.py"
+    path.write_text('raise RuntimeError("short")\n', encoding="utf-8")
+
+    m.run_on_file(str(path), max_string_length=100)
+
+    assert capsys.readouterr().out == ""
+
+
+def test_run_on_file_syntax_error(tmp_path, capsys):
+    path = tmp_path / "broken.py"
+    path.write_text("raise RuntimeError(\n", encoding="utf-8")
+
+    with pytest.raises(SystemExit) as exc:
+        m.run_on_file(str(path))
+
+    assert exc.value.code == 1
+    assert "Traceback:" in capsys.readouterr().out
+
+
+@pytest.mark.usefixtures("_reset_max_string_length")
+def test_main(tmp_path, capsys, monkeypatch):
+    path = tmp_path / "example.py"
+    path.write_text('raise RuntimeError("a long message")\n', encoding="utf-8")
+
+    monkeypatch.setattr(sys, "argv", ["flake8-errmsg", str(path)])
+    m.main()
+
+    assert "EM101" in capsys.readouterr().out

From 1815be00ba9d7a64b1477b57761f0abeeeab5749 Mon Sep 17 00:00:00 2001
From: Henry Schreiner <henryfs@princeton.edu>
Date: Mon, 15 Jun 2026 19:14:50 -0400
Subject: [PATCH 2/2] test: restore max_string_length in the existing
 test_string_length too

Fold the pre-existing test that mutated the class-level option into the
restoring fixture, so it no longer leaks state to later tests.

Assisted-by: ClaudeCode:claude-opus-4.8
---
 tests/test_package.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/test_package.py b/tests/test_package.py
index 347c788..fdf303e 100644
--- a/tests/test_package.py
+++ b/tests/test_package.py
@@ -36,6 +36,7 @@ def test_err1():
     )
 
 
+@pytest.mark.usefixtures("_reset_max_string_length")
 def test_string_length():
     node = ast.parse(ERR1)
     plugin = m.ErrMsgASTPlugin(node)