Rewrote form widget tests as proper unittests.

This is preparation for landing the template-based widget rendering
patch and goes a long way to making these tests more useful for future
development. The old doctest heritage is strong here.

tests/forms_tests/widget_tests/test_nullbooleanselect.py

@@ -0,0 +1,64 @@
+from django.forms import NullBooleanSelect
+from django.test import override_settings
+from django.utils import translation
+
+from .base import WidgetTest
+
+
+class NullBooleanSelectTest(WidgetTest):
+    widget = NullBooleanSelect()
+
+    def test_render_true(self):
+        self.check_html(self.widget, 'is_cool', True, html=(
+            """<select name="is_cool">
+            <option value="1">Unknown</option>
+            <option value="2" selected="selected">Yes</option>
+            <option value="3">No</option>
+            </select>"""
+        ))
+
+    def test_render_false(self):
+        self.check_html(self.widget, 'is_cool', False, html=(
+            """<select name="is_cool">
+            <option value="1">Unknown</option>
+            <option value="2">Yes</option>
+            <option value="3" selected="selected">No</option>
+            </select>"""
+        ))
+
+    def test_render_none(self):
+        self.check_html(self.widget, 'is_cool', None, html=(
+            """<select name="is_cool">
+            <option value="1" selected="selected">Unknown</option>
+            <option value="2">Yes</option>
+            <option value="3">No</option>
+            </select>"""
+        ))
+
+    def test_render_value(self):
+        self.check_html(self.widget, 'is_cool', '2', html=(
+            """<select name="is_cool">
+            <option value="1">Unknown</option>
+            <option value="2" selected="selected">Yes</option>
+            <option value="3">No</option>
+            </select>"""
+        ))
+
+    @override_settings(USE_L10N=True)
+    def test_l10n(self):
+        """
+        Ensure that the NullBooleanSelect widget's options are lazily
+        localized (#17190).
+        """
+        widget = NullBooleanSelect()
+
+        with translation.override('de-at'):
+            self.check_html(widget, 'id_bool', True, html=(
+                """
+                <select name="id_bool">
+                    <option value="1">Unbekannt</option>
+                    <option value="2" selected="selected">Ja</option>
+                    <option value="3">Nein</option>
+                </select>
+                """
+            ))