remove --diff option

tests/integration/test_main.py

@@ -13,42 +13,6 @@ from flake8.main import cli
 from flake8.options import config
 
 
-def test_diff_option(tmpdir, capsys):
-    """Ensure that `flake8 --diff` works."""
-    t_py_contents = """\
-import os
-import sys  # unused but not part of diff
-
-print('(to avoid trailing whitespace in test)')
-print('(to avoid trailing whitespace in test)')
-print(os.path.join('foo', 'bar'))
-
-y  # part of the diff and an error
-"""
-
-    diff = """\
-diff --git a/t.py b/t.py
-index d64ac39..7d943de 100644
---- a/t.py
-+++ b/t.py
-@@ -4,3 +4,5 @@ import sys  # unused but not part of diff
- print('(to avoid trailing whitespace in test)')
- print('(to avoid trailing whitespace in test)')
- print(os.path.join('foo', 'bar'))
-+
-+y  # part of the diff and an error
-"""
-
-    with mock.patch.object(utils, "stdin_get_value", return_value=diff):
-        with tmpdir.as_cwd():
-            tmpdir.join("t.py").write(t_py_contents)
-            assert cli.main(["--diff"]) == 1
-
-    out, err = capsys.readouterr()
-    assert out == "t.py:8:1: F821 undefined name 'y'\n"
-    assert err == ""
-
-
 def test_form_feed_line_split(tmpdir, capsys):
     """Test that form feed is treated the same for stdin."""
     src = "x=1\n\f\ny=1\n"