Write a test checking plugin failure exception handling

tests/unit/conftest.py

@@ -0,0 +1,17 @@
+"""Shared fixtures between unit tests"""
+import pytest
+import optparse
+
+def options_from(**kwargs):
+    """Generate a Values instances with our kwargs."""
+    kwargs.setdefault('hang_closing', True)
+    kwargs.setdefault('max_line_length', 79)
+    kwargs.setdefault('verbose', False)
+    kwargs.setdefault('stdin_display_name', 'stdin')
+    return optparse.Values(kwargs)
+
+@pytest.fixture
+def default_options():
+    """Fixture returning the default options of flake8"""
+    return options_from()
+    

tests/unit/test_file_checker.py

@@ -1,5 +1,7 @@
 """Unit tests for the FileChecker class."""
 import mock
+import pytest
+import flake8
 
 from flake8 import checker
 
@@ -43,3 +45,19 @@ def test_nonexistent_file():
     assert len(c.results) == 1
     error = c.results[0]
     assert error[0] == "E902"
+
+
+def test_raises_proper_exception_on_failed_plugin_run(tmp_path, default_options):
+    foobar = tmp_path / 'foobar.py'
+    foobar.write_text("I exist")
+    plugin = {
+        "name": "failure",
+        "plugin_name": "failure",  # Both are necessary
+        "parameters": dict(),
+        "plugin": mock.MagicMock(side_effect=ValueError),
+    }
+    """Verify a failing plugin results in an plugin error"""
+    fchecker = checker.FileChecker(
+        str(foobar), checks=[], options=default_options)
+    with pytest.raises(flake8.exceptions.PluginExecutionFailed):
+        fchecker.run_check(plugin)