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_dateinput.py

@@ -0,0 +1,47 @@
+from datetime import date
+
+from django.forms import DateInput
+from django.test import override_settings
+from django.utils import translation
+
+from .base import WidgetTest
+
+
+class DateInputTest(WidgetTest):
+    widget = DateInput()
+
+    def test_render_none(self):
+        self.check_html(self.widget, 'date', None, html='<input type="text" name="date" />')
+
+    def test_render_value(self):
+        d = date(2007, 9, 17)
+        self.assertEqual(str(d), '2007-09-17')
+
+        self.check_html(self.widget, 'date', d, html='<input type="text" name="date" value="2007-09-17" />')
+        self.check_html(self.widget, 'date', date(2007, 9, 17), html=(
+            '<input type="text" name="date" value="2007-09-17" />'
+        ))
+
+    def test_string(self):
+        """
+        Should be able to initialize from a string value.
+        """
+        self.check_html(self.widget, 'date', '2007-09-17', html=(
+            '<input type="text" name="date" value="2007-09-17" />'
+        ))
+
+    def test_format(self):
+        """
+        Use 'format' to change the way a value is displayed.
+        """
+        d = date(2007, 9, 17)
+        widget = DateInput(format='%d/%m/%Y', attrs={'type': 'date'})
+        self.check_html(widget, 'date', d, html='<input type="date" name="date" value="17/09/2007" />')
+
+    @override_settings(USE_L10N=True)
+    @translation.override('de-at')
+    def test_l10n(self):
+        self.check_html(
+            self.widget, 'date', date(2007, 9, 17),
+            html='<input type="text" name="date" value="17.09.2007" />',
+        )