diff --git a/src/flake8/api/legacy.py b/src/flake8/api/legacy.py
index 0aec7d9..8c7d337 100644
--- a/src/flake8/api/legacy.py
+++ b/src/flake8/api/legacy.py
@@ -115,8 +115,9 @@ class StyleGuide(object):
 
     def init_report(self, reporter=None):
         """Set up a formatter for this run of Flake8."""
-        if (reporter is not None and
-                not issubclass(reporter, formatter.BaseFormatter)):
+        if reporter is None:
+            return
+        if not issubclass(reporter, formatter.BaseFormatter):
             raise ValueError("Report should be subclass of "
                              "flake8.formatter.BaseFormatter.")
         self._application.make_formatter(reporter)
diff --git a/tests/unit/test_legacy_api.py b/tests/unit/test_legacy_api.py
new file mode 100644
index 0000000..0f1d1f3
--- /dev/null
+++ b/tests/unit/test_legacy_api.py
@@ -0,0 +1,145 @@
+"""Tests for Flake8's legacy API."""
+import mock
+import pytest
+
+from flake8.api import legacy as api
+from flake8.formatting import base as formatter
+
+
+def test_get_style_guide():
+    """Verify the methods called on our internal Application."""
+    mockedapp = mock.Mock()
+    with mock.patch('flake8.main.application.Application') as Application:
+        Application.return_value = mockedapp
+        style_guide = api.get_style_guide()
+
+    Application.assert_called_once_with()
+    mockedapp.find_plugins.assert_called_once_with()
+    mockedapp.register_plugin_options.assert_called_once_with()
+    mockedapp.parse_configuration_and_cli.assert_called_once_with([])
+    mockedapp.make_formatter.assert_called_once_with()
+    mockedapp.make_notifier.assert_called_once_with()
+    mockedapp.make_guide.assert_called_once_with()
+    mockedapp.make_file_checker_manager.assert_called_once_with()
+    assert isinstance(style_guide, api.StyleGuide)
+
+
+def test_styleguide_options():
+    """Show tha we proxy the StyleGuide.options attribute."""
+    app = mock.Mock()
+    app.options = 'options'
+    style_guide = api.StyleGuide(app)
+    assert style_guide.options == 'options'
+
+
+def test_styleguide_paths():
+    """Show tha we proxy the StyleGuide.paths attribute."""
+    app = mock.Mock()
+    app.paths = 'paths'
+    style_guide = api.StyleGuide(app)
+    assert style_guide.paths == 'paths'
+
+
+def test_styleguide_check_files():
+    """Verify we call the right application methods."""
+    paths = ['foo', 'bar']
+    app = mock.Mock()
+    style_guide = api.StyleGuide(app)
+    report = style_guide.check_files(paths)
+
+    app.run_checks.assert_called_once_with(paths)
+    app.report_errors.assert_called_once_with()
+    assert isinstance(report, api.Report)
+
+
+def test_styleguide_excluded():
+    """Verify we delegate to our file checker manager.
+
+    We also want to ensure that if we don't specify a parent, is_path_excluded
+    is called exactly once.
+    """
+    app = mock.Mock()
+    file_checker_manager = app.file_checker_manager = mock.Mock()
+    style_guide = api.StyleGuide(app)
+
+    style_guide.excluded('file.py')
+    file_checker_manager.is_path_excluded.assert_called_once_with('file.py')
+
+
+def test_styleguide_excluded_with_parent():
+    """Verify we delegate to our file checker manager.
+
+    When we add the parent argument, we don't check that is_path_excluded was
+    called only once.
+    """
+    app = mock.Mock()
+    file_checker_manager = app.file_checker_manager = mock.Mock()
+    style_guide = api.StyleGuide(app)
+
+    style_guide.excluded('file.py', 'parent')
+    file_checker_manager.is_path_excluded.call_args == [
+        ('file.py',),
+        ('parent/file.py',),
+    ]
+
+
+def test_styleguide_init_report_does_nothing():
+    """Verify if we use None that we don't call anything."""
+    app = mock.Mock()
+    style_guide = api.StyleGuide(app)
+    style_guide.init_report()
+    assert app.make_formatter.called is False
+    assert app.make_guide.called is False
+
+
+def test_styleguide_init_report_with_non_subclass():
+    """Verify we raise a ValueError with non BaseFormatter subclasses."""
+    app = mock.Mock()
+    style_guide = api.StyleGuide(app)
+    with pytest.raises(ValueError):
+        style_guide.init_report(object)
+    assert app.make_formatter.called is False
+    assert app.make_guide.called is False
+
+
+def test_styleguide_init_report():
+    """Verify we do the right incantation for the Application."""
+    app = mock.Mock(guide='fake')
+    style_guide = api.StyleGuide(app)
+
+    class FakeFormatter(formatter.BaseFormatter):
+        def format(self, *args):
+            pass
+
+    style_guide.init_report(FakeFormatter)
+    app.make_formatter.assert_called_once_with(FakeFormatter)
+    assert app.guide is None
+    app.make_guide.assert_called_once_with()
+
+
+def test_styleguide_input_file():
+    """Verify we call StyleGuide.check_files with the filename."""
+    app = mock.Mock()
+    style_guide = api.StyleGuide(app)
+    with mock.patch.object(style_guide, 'check_files') as check_files:
+        style_guide.input_file('file.py')
+    check_files.assert_called_once_with(['file.py'])
+
+
+def test_report_total_errors():
+    """Verify total errors is just a proxy attribute."""
+    app = mock.Mock(result_count='Fake count')
+    report = api.Report(app)
+    assert report.total_errors == 'Fake count'
+
+
+def test_report_get_statistics():
+    """Verify that we use the statistics object."""
+    stats = mock.Mock()
+    stats.statistics_for.return_value = []
+    style_guide = mock.Mock(stats=stats)
+    app = mock.Mock(guide=style_guide)
+
+    report = api.Report(app)
+    assert report.get_statistics('E') == []
+    stats.statistics_for.assert_called_once_with('E')