Merge branch 'refactor-decision-engine' into 'master'

Refactor decision logic into its own object

See merge request !190

7 files changed, 252 insertions, 234 deletions

diff --git a/tests/unit/test_base_formatter.py b/tests/unit/test_base_formatter.py
index bb54358..87b5fee 100644
--- a/tests/unit/test_base_formatter.py
+++ b/tests/unit/test_base_formatter.py
@@ -51,7 +51,7 @@ def test_show_source_returns_nothing_when_not_showing_source():
     """Ensure we return nothing when users want nothing."""
     formatter = base.BaseFormatter(options(show_source=False))
     assert formatter.show_source(
-        style_guide.Error('A000', 'file.py', 1, 1, 'error text', 'line')
+        style_guide.Violation('A000', 'file.py', 1, 1, 'error text', 'line')
     ) is ''
 
 
@@ -59,7 +59,7 @@ def test_show_source_returns_nothing_when_there_is_source():
     """Ensure we return nothing when there is no line."""
     formatter = base.BaseFormatter(options(show_source=True))
     assert formatter.show_source(
-        style_guide.Error('A000', 'file.py', 1, 1, 'error text', None)
+        style_guide.Violation('A000', 'file.py', 1, 1, 'error text', None)
     ) is ''
 
 
@@ -71,7 +71,7 @@ def test_show_source_returns_nothing_when_there_is_source():
 def test_show_source_updates_physical_line_appropriately(line, column):
     """Ensure the error column is appropriately indicated."""
     formatter = base.BaseFormatter(options(show_source=True))
-    error = style_guide.Error('A000', 'file.py', 1, column, 'error', line)
+    error = style_guide.Violation('A000', 'file.py', 1, column, 'error', line)
     output = formatter.show_source(error)
     _, pointer = output.rsplit('\n', 1)
     assert pointer.count(' ') == (column - 1)
@@ -149,7 +149,7 @@ def test_handle_formats_the_error():
     """Verify that a formatter will call format from handle."""
     formatter = FormatFormatter(options(show_source=False))
     filemock = formatter.output_fd = mock.Mock()
-    error = style_guide.Error(
+    error = style_guide.Violation(
         code='A001',
         filename='example.py',
         line_number=1,
diff --git a/tests/unit/test_decision_engine.py b/tests/unit/test_decision_engine.py
new file mode 100644
index 0000000..db9c270
--- /dev/null
+++ b/tests/unit/test_decision_engine.py
@@ -0,0 +1,184 @@
+"""Tests for the flake8.style_guide.DecisionEngine class."""
+import optparse
+
+import pytest
+
+from flake8 import defaults
+from flake8 import style_guide
+
+
+def create_options(**kwargs):
+    """Create and return an instance of optparse.Values."""
+    kwargs.setdefault('select', [])
+    kwargs.setdefault('extended_default_select', [])
+    kwargs.setdefault('ignore', [])
+    kwargs.setdefault('disable_noqa', False)
+    kwargs.setdefault('enable_extensions', [])
+    return optparse.Values(kwargs)
+
+
+@pytest.mark.parametrize('ignore_list,error_code', [
+    (['E111', 'E121'], 'E111'),
+    (['E111', 'E121'], 'E121'),
+    (['E11', 'E12'], 'E121'),
+    (['E2', 'E12'], 'E121'),
+    (['E2', 'E12'], 'E211'),
+])
+def test_was_ignored_ignores_errors(ignore_list, error_code):
+    """Verify we detect users explicitly ignoring an error."""
+    decider = style_guide.DecisionEngine(create_options(ignore=ignore_list))
+
+    assert decider.was_ignored(error_code) is style_guide.Ignored.Explicitly
+
+
+@pytest.mark.parametrize('ignore_list,error_code', [
+    (['E111', 'E121'], 'E112'),
+    (['E111', 'E121'], 'E122'),
+    (['E11', 'E12'], 'W121'),
+    (['E2', 'E12'], 'E112'),
+    (['E2', 'E12'], 'E111'),
+])
+def test_was_ignored_implicitly_selects_errors(ignore_list, error_code):
+    """Verify we detect users does not explicitly ignore an error."""
+    decider = style_guide.DecisionEngine(create_options(ignore=ignore_list))
+
+    assert decider.was_ignored(error_code) is style_guide.Selected.Implicitly
+
+
+@pytest.mark.parametrize('select_list,enable_extensions,error_code', [
+    (['E111', 'E121'], [], 'E111'),
+    (['E111', 'E121'], [], 'E121'),
+    (['E11', 'E12'], [], 'E121'),
+    (['E2', 'E12'], [], 'E121'),
+    (['E2', 'E12'], [], 'E211'),
+    (['E1'], ['E2'], 'E211'),
+    ([], ['E2'], 'E211'),
+])
+def test_was_selected_selects_errors(select_list, enable_extensions,
+                                     error_code):
+    """Verify we detect users explicitly selecting an error."""
+    decider = style_guide.DecisionEngine(
+        options=create_options(select=select_list,
+                               enable_extensions=enable_extensions),
+    )
+
+    assert decider.was_selected(error_code) is style_guide.Selected.Explicitly
+
+
+def test_was_selected_implicitly_selects_errors():
+    """Verify we detect users implicitly selecting an error."""
+    select_list = []
+    error_code = 'E121'
+    decider = style_guide.DecisionEngine(
+        create_options(
+            select=select_list,
+            extended_default_select=['E'],
+        ),
+    )
+
+    assert decider.was_selected(error_code) is style_guide.Selected.Implicitly
+
+
+@pytest.mark.parametrize('select_list,error_code', [
+    (['E111', 'E121'], 'E112'),
+    (['E111', 'E121'], 'E122'),
+    (['E11', 'E12'], 'E132'),
+    (['E2', 'E12'], 'E321'),
+    (['E2', 'E12'], 'E410'),
+])
+def test_was_selected_excludes_errors(select_list, error_code):
+    """Verify we detect users implicitly excludes an error."""
+    decider = style_guide.DecisionEngine(create_options(select=select_list))
+
+    assert decider.was_selected(error_code) is style_guide.Ignored.Implicitly
+
+
+@pytest.mark.parametrize('select_list,ignore_list,error_code,expected', [
+    (['E111', 'E121'], [], 'E111', style_guide.Decision.Selected),
+    (['E111', 'E121'], [], 'E112', style_guide.Decision.Ignored),
+    (['E111', 'E121'], [], 'E121', style_guide.Decision.Selected),
+    (['E111', 'E121'], [], 'E122', style_guide.Decision.Ignored),
+    (['E11', 'E12'], [], 'E132', style_guide.Decision.Ignored),
+    (['E2', 'E12'], [], 'E321', style_guide.Decision.Ignored),
+    (['E2', 'E12'], [], 'E410', style_guide.Decision.Ignored),
+    (['E11', 'E121'], ['E1'], 'E112', style_guide.Decision.Selected),
+    (['E111', 'E121'], ['E2'], 'E122', style_guide.Decision.Ignored),
+    (['E11', 'E12'], ['E13'], 'E132', style_guide.Decision.Ignored),
+    (['E1', 'E3'], ['E32'], 'E321', style_guide.Decision.Ignored),
+    ([], ['E2', 'E12'], 'E410', style_guide.Decision.Ignored),
+    (['E4'], ['E2', 'E12', 'E41'], 'E410', style_guide.Decision.Ignored),
+    (['E41'], ['E2', 'E12', 'E4'], 'E410', style_guide.Decision.Selected),
+    (['E'], ['F'], 'E410', style_guide.Decision.Selected),
+    (['F'], [], 'E410', style_guide.Decision.Ignored),
+    (['E'], defaults.IGNORE, 'E126', style_guide.Decision.Selected),
+    (['W'], defaults.IGNORE, 'E126', style_guide.Decision.Ignored),
+    (['E'], defaults.IGNORE, 'W391', style_guide.Decision.Ignored),
+    (['E', 'W'], ['E13'], 'E131', style_guide.Decision.Ignored),
+    (defaults.SELECT, ['E13'], 'E131', style_guide.Decision.Ignored),
+    (defaults.SELECT, defaults.IGNORE, 'E126', style_guide.Decision.Ignored),
+    (defaults.SELECT, defaults.IGNORE, 'W391', style_guide.Decision.Selected),
+])
+def test_decision_for(select_list, ignore_list, error_code, expected):
+    """Verify we decide when to report an error."""
+    decider = style_guide.DecisionEngine(create_options(select=select_list,
+                                                        ignore=ignore_list))
+
+    assert decider.decision_for(error_code) is expected
+
+
+@pytest.mark.parametrize(
+    'select,ignore,extend_select,enabled_extensions,error_code,expected', [
+        (defaults.SELECT, [], ['I1'], [], 'I100',
+            style_guide.Decision.Selected),
+        (defaults.SELECT, [], ['I1'], [], 'I201',
+            style_guide.Decision.Ignored),
+        (defaults.SELECT, ['I2'], ['I1'], [], 'I101',
+            style_guide.Decision.Selected),
+        (defaults.SELECT, ['I2'], ['I1'], [], 'I201',
+            style_guide.Decision.Ignored),
+        (defaults.SELECT, ['I1'], ['I10'], [], 'I101',
+            style_guide.Decision.Selected),
+        (defaults.SELECT, ['I10'], ['I1'], [], 'I101',
+            style_guide.Decision.Ignored),
+        (defaults.SELECT, [], [], ['U4'], 'U401',
+            style_guide.Decision.Selected),
+        (defaults.SELECT, ['U401'], [], ['U4'], 'U401',
+            style_guide.Decision.Ignored),
+        (defaults.SELECT, ['U401'], [], ['U4'], 'U402',
+            style_guide.Decision.Selected),
+        (['E', 'W'], ['E13'], [], [], 'E131', style_guide.Decision.Ignored),
+        (['E', 'W'], ['E13'], [], [], 'E126', style_guide.Decision.Selected),
+        (['E2'], ['E21'], [], [], 'E221', style_guide.Decision.Selected),
+        (['E2'], ['E21'], [], [], 'E212', style_guide.Decision.Ignored),
+        (['F', 'W'], ['C90'], ['I1'], [], 'C901',
+            style_guide.Decision.Ignored),
+        (['E', 'W'], ['C'], [], [], 'E131',
+            style_guide.Decision.Selected),
+        (defaults.SELECT, defaults.IGNORE, [], ['I'], 'I101',
+            style_guide.Decision.Selected),
+        (defaults.SELECT, defaults.IGNORE, ['G'], ['I'], 'G101',
+            style_guide.Decision.Selected),
+        (defaults.SELECT, ['G1'], ['G'], ['I'], 'G101',
+            style_guide.Decision.Ignored),
+        (defaults.SELECT, ['E126'], [], ['I'], 'I101',
+            style_guide.Decision.Selected),
+        # This next one should exercise the catch-all return and yes, this is
+        # a *very* odd combination but users find much odder combinations
+        # anyway.
+        (['E', 'W'], defaults.IGNORE, ['I'], [], 'I101',
+            style_guide.Decision.Selected),
+    ]
+)
+def test_more_specific_decision_for_logic(select, ignore, extend_select,
+                                          enabled_extensions, error_code,
+                                          expected):
+    """Verify the logic of DecisionEngine.more_specific_decision_for."""
+    decider = style_guide.DecisionEngine(
+        create_options(
+            select=select, ignore=ignore,
+            extended_default_select=extend_select,
+            enable_extensions=enabled_extensions,
+        ),
+    )
+
+    assert decider.more_specific_decision_for(error_code) is expected
diff --git a/tests/unit/test_filenameonly_formatter.py b/tests/unit/test_filenameonly_formatter.py
index caa0ae3..b423ee3 100644
--- a/tests/unit/test_filenameonly_formatter.py
+++ b/tests/unit/test_filenameonly_formatter.py
@@ -17,14 +17,15 @@ def test_caches_filenames_already_printed():
     formatter = default.FilenameOnly(options())
     assert formatter.filenames_already_printed == set()
 
-    formatter.format(style_guide.Error('code', 'file.py', 1, 1, 'text', 'l'))
+    formatter.format(
+        style_guide.Violation('code', 'file.py', 1, 1, 'text', 'l'))
     assert formatter.filenames_already_printed == {'file.py'}
 
 
 def test_only_returns_a_string_once_from_format():
     """Verify format ignores the second error with the same filename."""
     formatter = default.FilenameOnly(options())
-    error = style_guide.Error('code', 'file.py', 1, 1, 'text', '1')
+    error = style_guide.Violation('code', 'file.py', 1, 1, 'text', '1')
 
     assert formatter.format(error) == 'file.py'
     assert formatter.format(error) is None
@@ -33,6 +34,6 @@ def test_only_returns_a_string_once_from_format():
 def test_show_source_returns_nothing():
     """Verify show_source returns nothing."""
     formatter = default.FilenameOnly(options())
-    error = style_guide.Error('code', 'file.py', 1, 1, 'text', '1')
+    error = style_guide.Violation('code', 'file.py', 1, 1, 'text', '1')
 
     assert formatter.show_source(error) is None
diff --git a/tests/unit/test_nothing_formatter.py b/tests/unit/test_nothing_formatter.py
index ce8087f..a1fd683 100644
--- a/tests/unit/test_nothing_formatter.py
+++ b/tests/unit/test_nothing_formatter.py
@@ -15,7 +15,7 @@ def options(**kwargs):
 def test_format_returns_nothing():
     """Verify Nothing.format returns None."""
     formatter = default.Nothing(options())
-    error = style_guide.Error('code', 'file.py', 1, 1, 'text', '1')
+    error = style_guide.Violation('code', 'file.py', 1, 1, 'text', '1')
 
     assert formatter.format(error) is None
 
@@ -23,6 +23,6 @@ def test_format_returns_nothing():
 def test_show_source_returns_nothing():
     """Verify Nothing.show_source returns None."""
     formatter = default.Nothing(options())
-    error = style_guide.Error('code', 'file.py', 1, 1, 'text', '1')
+    error = style_guide.Violation('code', 'file.py', 1, 1, 'text', '1')
 
     assert formatter.show_source(error) is None
diff --git a/tests/unit/test_statistics.py b/tests/unit/test_statistics.py
index f95c638..31d6276 100644
--- a/tests/unit/test_statistics.py
+++ b/tests/unit/test_statistics.py
@@ -11,7 +11,7 @@ DEFAULT_TEXT = 'Default text'
 
 def make_error(**kwargs):
     """Create errors with a bunch of default values."""
-    return style_guide.Error(
+    return style_guide.Violation(
         code=kwargs.pop('code', DEFAULT_ERROR_CODE),
         filename=kwargs.pop('filename', DEFAULT_FILENAME),
         line_number=kwargs.pop('line_number', 1),
diff --git a/tests/unit/test_style_guide.py b/tests/unit/test_style_guide.py
index 5c24048..84c47ff 100644
--- a/tests/unit/test_style_guide.py
+++ b/tests/unit/test_style_guide.py
@@ -4,7 +4,6 @@ import optparse
 import mock
 import pytest
 
-from flake8 import defaults
 from flake8 import style_guide
 from flake8.formatting import base
 from flake8.plugins import notifier
@@ -20,227 +19,6 @@ def create_options(**kwargs):
     return optparse.Values(kwargs)
 
 
-@pytest.mark.parametrize('ignore_list,error_code', [
-    (['E111', 'E121'], 'E111'),
-    (['E111', 'E121'], 'E121'),
-    (['E11', 'E12'], 'E121'),
-    (['E2', 'E12'], 'E121'),
-    (['E2', 'E12'], 'E211'),
-])
-def test_is_user_ignored_ignores_errors(ignore_list, error_code):
-    """Verify we detect users explicitly ignoring an error."""
-    guide = style_guide.StyleGuide(create_options(ignore=ignore_list),
-                                   listener_trie=None,
-                                   formatter=None)
-
-    assert guide.is_user_ignored(error_code) is style_guide.Ignored.Explicitly
-
-
-@pytest.mark.parametrize('ignore_list,error_code', [
-    (['E111', 'E121'], 'E112'),
-    (['E111', 'E121'], 'E122'),
-    (['E11', 'E12'], 'W121'),
-    (['E2', 'E12'], 'E112'),
-    (['E2', 'E12'], 'E111'),
-])
-def test_is_user_ignored_implicitly_selects_errors(ignore_list, error_code):
-    """Verify we detect users does not explicitly ignore an error."""
-    guide = style_guide.StyleGuide(create_options(ignore=ignore_list),
-                                   listener_trie=None,
-                                   formatter=None)
-
-    assert guide.is_user_ignored(error_code) is style_guide.Selected.Implicitly
-
-
-@pytest.mark.parametrize('select_list,enable_extensions,error_code', [
-    (['E111', 'E121'], [], 'E111'),
-    (['E111', 'E121'], [], 'E121'),
-    (['E11', 'E12'], [], 'E121'),
-    (['E2', 'E12'], [], 'E121'),
-    (['E2', 'E12'], [], 'E211'),
-    (['E1'], ['E2'], 'E211'),
-    ([], ['E2'], 'E211'),
-])
-def test_is_user_selected_selects_errors(select_list, enable_extensions,
-                                         error_code):
-    """Verify we detect users explicitly selecting an error."""
-    guide = style_guide.StyleGuide(
-        options=create_options(select=select_list,
-                               enable_extensions=enable_extensions),
-        listener_trie=None,
-        formatter=None,
-    )
-
-    assert (guide.is_user_selected(error_code) is
-            style_guide.Selected.Explicitly)
-
-
-def test_is_user_selected_implicitly_selects_errors():
-    """Verify we detect users implicitly selecting an error."""
-    select_list = []
-    error_code = 'E121'
-    guide = style_guide.StyleGuide(
-        create_options(
-            select=select_list,
-            extended_default_select=['E'],
-        ),
-        listener_trie=None,
-        formatter=None,
-    )
-
-    assert (guide.is_user_selected(error_code) is
-            style_guide.Selected.Implicitly)
-
-
-@pytest.mark.parametrize('select_list,error_code', [
-    (['E111', 'E121'], 'E112'),
-    (['E111', 'E121'], 'E122'),
-    (['E11', 'E12'], 'E132'),
-    (['E2', 'E12'], 'E321'),
-    (['E2', 'E12'], 'E410'),
-])
-def test_is_user_selected_excludes_errors(select_list, error_code):
-    """Verify we detect users implicitly excludes an error."""
-    guide = style_guide.StyleGuide(create_options(select=select_list),
-                                   listener_trie=None,
-                                   formatter=None)
-
-    assert guide.is_user_selected(error_code) is style_guide.Ignored.Implicitly
-
-
-@pytest.mark.parametrize('select_list,ignore_list,error_code,expected', [
-    (['E111', 'E121'], [], 'E111', style_guide.Decision.Selected),
-    (['E111', 'E121'], [], 'E112', style_guide.Decision.Ignored),
-    (['E111', 'E121'], [], 'E121', style_guide.Decision.Selected),
-    (['E111', 'E121'], [], 'E122', style_guide.Decision.Ignored),
-    (['E11', 'E12'], [], 'E132', style_guide.Decision.Ignored),
-    (['E2', 'E12'], [], 'E321', style_guide.Decision.Ignored),
-    (['E2', 'E12'], [], 'E410', style_guide.Decision.Ignored),
-    (['E11', 'E121'], ['E1'], 'E112', style_guide.Decision.Selected),
-    (['E111', 'E121'], ['E2'], 'E122', style_guide.Decision.Ignored),
-    (['E11', 'E12'], ['E13'], 'E132', style_guide.Decision.Ignored),
-    (['E1', 'E3'], ['E32'], 'E321', style_guide.Decision.Ignored),
-    ([], ['E2', 'E12'], 'E410', style_guide.Decision.Ignored),
-    (['E4'], ['E2', 'E12', 'E41'], 'E410', style_guide.Decision.Ignored),
-    (['E41'], ['E2', 'E12', 'E4'], 'E410', style_guide.Decision.Selected),
-    (['E'], ['F'], 'E410', style_guide.Decision.Selected),
-    (['F'], [], 'E410', style_guide.Decision.Ignored),
-    (['E'], defaults.IGNORE, 'E126', style_guide.Decision.Selected),
-    (['W'], defaults.IGNORE, 'E126', style_guide.Decision.Ignored),
-    (['E'], defaults.IGNORE, 'W391', style_guide.Decision.Ignored),
-    (['E', 'W'], ['E13'], 'E131', style_guide.Decision.Ignored),
-    (defaults.SELECT, ['E13'], 'E131', style_guide.Decision.Ignored),
-    (defaults.SELECT, defaults.IGNORE, 'E126', style_guide.Decision.Ignored),
-    (defaults.SELECT, defaults.IGNORE, 'W391', style_guide.Decision.Selected),
-])
-def test_should_report_error(select_list, ignore_list, error_code, expected):
-    """Verify we decide when to report an error."""
-    guide = style_guide.StyleGuide(create_options(select=select_list,
-                                                  ignore=ignore_list),
-                                   listener_trie=None,
-                                   formatter=None)
-
-    assert guide.should_report_error(error_code) is expected
-
-
-@pytest.mark.parametrize(
-    'select,ignore,extend_select,enabled_extensions,error_code,expected', [
-        (defaults.SELECT, [], ['I1'], [], 'I100',
-            style_guide.Decision.Selected),
-        (defaults.SELECT, [], ['I1'], [], 'I201',
-            style_guide.Decision.Ignored),
-        (defaults.SELECT, ['I2'], ['I1'], [], 'I101',
-            style_guide.Decision.Selected),
-        (defaults.SELECT, ['I2'], ['I1'], [], 'I201',
-            style_guide.Decision.Ignored),
-        (defaults.SELECT, ['I1'], ['I10'], [], 'I101',
-            style_guide.Decision.Selected),
-        (defaults.SELECT, ['I10'], ['I1'], [], 'I101',
-            style_guide.Decision.Ignored),
-        (defaults.SELECT, [], [], ['U4'], 'U401',
-            style_guide.Decision.Selected),
-        (defaults.SELECT, ['U401'], [], ['U4'], 'U401',
-            style_guide.Decision.Ignored),
-        (defaults.SELECT, ['U401'], [], ['U4'], 'U402',
-            style_guide.Decision.Selected),
-        (['E', 'W'], ['E13'], [], [], 'E131', style_guide.Decision.Ignored),
-        (['E', 'W'], ['E13'], [], [], 'E126', style_guide.Decision.Selected),
-        (['E2'], ['E21'], [], [], 'E221', style_guide.Decision.Selected),
-        (['E2'], ['E21'], [], [], 'E212', style_guide.Decision.Ignored),
-        (['F', 'W'], ['C90'], ['I1'], [], 'C901',
-            style_guide.Decision.Ignored),
-        (['E', 'W'], ['C'], [], [], 'E131',
-            style_guide.Decision.Selected),
-        (defaults.SELECT, defaults.IGNORE, [], ['I'], 'I101',
-            style_guide.Decision.Selected),
-        (defaults.SELECT, defaults.IGNORE, ['G'], ['I'], 'G101',
-            style_guide.Decision.Selected),
-        (defaults.SELECT, ['G1'], ['G'], ['I'], 'G101',
-            style_guide.Decision.Ignored),
-        (defaults.SELECT, ['E126'], [], ['I'], 'I101',
-            style_guide.Decision.Selected),
-    ]
-)
-def test_decision_for_logic(select, ignore, extend_select, enabled_extensions,
-                            error_code, expected):
-    """Verify the complicated logic of StyleGuide._decision_for.
-
-    I usually avoid testing private methods, but this one is very important in
-    our conflict resolution work in Flake8.
-    """
-    guide = style_guide.StyleGuide(
-        create_options(
-            select=select, ignore=ignore,
-            extended_default_select=extend_select,
-            enable_extensions=enabled_extensions,
-        ),
-        listener_trie=None,
-        formatter=None,
-    )
-
-    assert guide._decision_for(error_code) is expected
-
-
-@pytest.mark.parametrize('error_code,physical_line,expected_result', [
-    ('E111', 'a = 1', False),
-    ('E121', 'a = 1  # noqa: E111', False),
-    ('E121', 'a = 1  # noqa: E111,W123,F821', False),
-    ('E111', 'a = 1  # noqa: E111,W123,F821', True),
-    ('W123', 'a = 1  # noqa: E111,W123,F821', True),
-    ('E111', 'a = 1  # noqa: E11,W123,F821', True),
-    ('E111', 'a = 1  # noqa, analysis:ignore', True),
-    ('E111', 'a = 1  # noqa analysis:ignore', True),
-    ('E111', 'a = 1  # noqa - We do not care', True),
-    ('E111', 'a = 1  # noqa: We do not care', True),
-])
-def test_is_inline_ignored(error_code, physical_line, expected_result):
-    """Verify that we detect inline usage of ``# noqa``."""
-    guide = style_guide.StyleGuide(create_options(select=['E', 'W', 'F']),
-                                   listener_trie=None,
-                                   formatter=None)
-    error = style_guide.Error(error_code, 'filename.py', 1, 1, 'error text',
-                              None)
-    # We want `None` to be passed as the physical line so we actually use our
-    # monkey-patched linecache.getline value.
-
-    with mock.patch('linecache.getline', return_value=physical_line):
-        assert guide.is_inline_ignored(error) is expected_result
-
-
-def test_disable_is_inline_ignored():
-    """Verify that is_inline_ignored exits immediately if disabling NoQA."""
-    guide = style_guide.StyleGuide(create_options(disable_noqa=True),
-                                   listener_trie=None,
-                                   formatter=None)
-    error = style_guide.Error('E121', 'filename.py', 1, 1, 'error text',
-                              'line')
-
-    with mock.patch('linecache.getline') as getline:
-        assert guide.is_inline_ignored(error) is False
-
-    assert getline.called is False
-
-
 @pytest.mark.parametrize('select_list,ignore_list,error_code', [
     (['E111', 'E121'], [], 'E111'),
     (['E111', 'E121'], [], 'E121'),
@@ -258,8 +36,8 @@ def test_handle_error_notifies_listeners(select_list, ignore_list, error_code):
 
     with mock.patch('linecache.getline', return_value=''):
         guide.handle_error(error_code, 'stdin', 1, 0, 'error found')
-    error = style_guide.Error(error_code, 'stdin', 1, 1, 'error found',
-                              None)
+    error = style_guide.Violation(
+        error_code, 'stdin', 1, 1, 'error found', None)
     listener_trie.notify.assert_called_once_with(error_code, error)
     formatter.handle.assert_called_once_with(error)
 
diff --git a/tests/unit/test_violation.py b/tests/unit/test_violation.py
new file mode 100644
index 0000000..fa75278
--- /dev/null
+++ b/tests/unit/test_violation.py
@@ -0,0 +1,55 @@
+"""Tests for the flake8.style_guide.Violation class."""
+import mock
+import pytest
+
+from flake8 import style_guide
+
+
+@pytest.mark.parametrize('error_code,physical_line,expected_result', [
+    ('E111', 'a = 1', False),
+    ('E121', 'a = 1  # noqa: E111', False),
+    ('E121', 'a = 1  # noqa: E111,W123,F821', False),
+    ('E111', 'a = 1  # noqa: E111,W123,F821', True),
+    ('W123', 'a = 1  # noqa: E111,W123,F821', True),
+    ('E111', 'a = 1  # noqa: E11,W123,F821', True),
+    ('E111', 'a = 1  # noqa, analysis:ignore', True),
+    ('E111', 'a = 1  # noqa analysis:ignore', True),
+    ('E111', 'a = 1  # noqa - We do not care', True),
+    ('E111', 'a = 1  # noqa: We do not care', True),
+])
+def test_is_inline_ignored(error_code, physical_line, expected_result):
+    """Verify that we detect inline usage of ``# noqa``."""
+    error = style_guide.Violation(
+        error_code, 'filename.py', 1, 1, 'error text', None)
+    # We want `None` to be passed as the physical line so we actually use our
+    # monkey-patched linecache.getline value.
+
+    with mock.patch('linecache.getline', return_value=physical_line):
+        assert error.is_inline_ignored(False) is expected_result
+
+
+def test_disable_is_inline_ignored():
+    """Verify that is_inline_ignored exits immediately if disabling NoQA."""
+    error = style_guide.Violation(
+        'E121', 'filename.py', 1, 1, 'error text', 'line')
+
+    with mock.patch('linecache.getline') as getline:
+        assert error.is_inline_ignored(True) is False
+
+    assert getline.called is False
+
+
+@pytest.mark.parametrize('violation_file,violation_line,diff,expected', [
+    ('file.py', 10, {}, True),
+    ('file.py', 1, {'file.py': range(1, 2)}, True),
+    ('file.py', 10, {'file.py': range(1, 2)}, False),
+    ('file.py', 1, {'other.py': range(1, 2)}, False),
+    ('file.py', 10, {'other.py': range(1, 2)}, False),
+])
+def test_violation_is_in_diff(violation_file, violation_line, diff, expected):
+    """Verify that we find violations within a diff."""
+    violation = style_guide.Violation(
+        'E001', violation_file, violation_line, 1, 'warning', 'line',
+    )
+
+    assert violation.is_in(diff) is expected