improve coverage a bit

src/flake8/checker.py

@@ -3,6 +3,7 @@ import collections
 import errno
 import itertools
 import logging
+import multiprocessing.pool
 import signal
 import tokenize
 from typing import Dict
@@ -15,11 +16,6 @@ from flake8 import exceptions
 from flake8 import processor
 from flake8 import utils
 
-try:
-    import multiprocessing.pool
-except ImportError:
-    multiprocessing = None  # type: ignore
-
 Results = List[Tuple[str, int, int, str, Optional[str]]]
 
 LOG = logging.getLogger(__name__)
@@ -40,13 +36,6 @@ SERIAL_RETRY_ERRNOS = {
 }
 
 
-def _multiprocessing_is_fork() -> bool:
-    """Class state is only preserved when using the `fork` strategy."""
-    return bool(
-        multiprocessing and multiprocessing.get_start_method() == "fork"
-    )
-
-
 class Manager:
     """Manage the parallelism and checker instances for each plugin and file.
 
@@ -113,7 +102,9 @@ class Manager:
         # - we're processing a diff, which again does not work well with
         #   multiprocessing and which really shouldn't require multiprocessing
         # - the user provided some awful input
-        if not _multiprocessing_is_fork():
+
+        # class state is only preserved when using the `fork` strategy.
+        if multiprocessing.get_start_method() != "fork":
             LOG.warning(
                 "The multiprocessing module is not available. "
                 "Ignoring --jobs arguments."

tests/integration/test_main.py

@@ -227,6 +227,29 @@ def test_bug_report_successful(capsys):
     assert err == ""
 
 
+def test_benchmark_successful(tmp_path, capsys):
+    """Test that --benchmark does not crash."""
+    fname = tmp_path.joinpath("t.py")
+    fname.write_text("print('hello world')\n")
+
+    _call_main(["--benchmark", str(fname)])
+
+    out, err = capsys.readouterr()
+    parts = [line.split(maxsplit=1) for line in out.splitlines()]
+    assert parts == [
+        [mock.ANY, "seconds elapsed"],
+        ["1", "total logical lines processed"],
+        [mock.ANY, "logical lines processed per second"],
+        ["1", "total physical lines processed"],
+        [mock.ANY, "physical lines processed per second"],
+        ["5", "total tokens processed"],
+        [mock.ANY, "tokens processed per second"],
+        ["1", "total files processed"],
+        [mock.ANY, "files processed per second"],
+    ]
+    assert err == ""
+
+
 def test_specific_noqa_does_not_clobber_pycodestyle_noqa(tmpdir, capsys):
     """See https://github.com/pycqa/flake8/issues/1104."""
     with tmpdir.as_cwd():

tests/unit/test_checker_manager.py

@@ -1,5 +1,6 @@
 """Tests for the Manager object for FileCheckers."""
 import errno
+import multiprocessing
 from unittest import mock
 
 import pytest
@@ -37,8 +38,8 @@ def test_oserrors_cause_serial_fall_back():
     assert serial.call_count == 1
 
 
-@mock.patch("flake8.checker._multiprocessing_is_fork", return_value=True)
+@mock.patch.object(multiprocessing, "get_start_method", return_value="fork")
-def test_oserrors_are_reraised(is_windows):
+def test_oserrors_are_reraised(_):
     """Verify that unexpected OSErrors will cause the Manager to reraise."""
     err = OSError(errno.EAGAIN, "Ominous message")
     with mock.patch("_multiprocessing.SemLock", side_effect=err):
@@ -49,15 +50,30 @@ def test_oserrors_are_reraised(is_windows):
     assert serial.call_count == 0
 
 
-def test_multiprocessing_is_disabled():
+@mock.patch.object(multiprocessing, "get_start_method", return_value="spawn")
+def test_multiprocessing_is_disabled(_):
     """Verify not being able to import multiprocessing forces jobs to 0."""
     style_guide = style_guide_mock()
-    with mock.patch("flake8.checker.multiprocessing", None):
     manager = checker.Manager(style_guide, [], [])
     assert manager.jobs == 0
 
 
-def test_make_checkers():
+def test_multiprocessing_cpu_count_not_implemented():
+    """Verify that jobs is 0 if cpu_count is unavailable."""
+    style_guide = style_guide_mock()
+    style_guide.options.jobs = JobsArgument("auto")
+
+    with mock.patch.object(
+        multiprocessing,
+        "cpu_count",
+        side_effect=NotImplementedError,
+    ):
+        manager = checker.Manager(style_guide, [], [])
+    assert manager.jobs == 0
+
+
+@mock.patch.object(multiprocessing, "get_start_method", return_value="spawn")
+def test_make_checkers(_):
     """Verify that we create a list of FileChecker instances."""
     style_guide = style_guide_mock()
     files = ["file1", "file2"]
@@ -67,7 +83,6 @@ def test_make_checkers():
         "logical_line_plugins": [],
         "physical_line_plugins": [],
     }
-    with mock.patch("flake8.checker.multiprocessing", None):
     manager = checker.Manager(style_guide, files, checkplugins)
 
     with mock.patch("flake8.utils.filenames_from") as filenames_from: