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/base.py

@@ -0,0 +1,9 @@
+from django.test import SimpleTestCase
+
+
+class WidgetTest(SimpleTestCase):
+    beatles = (('J', 'John'), ('P', 'Paul'), ('G', 'George'), ('R', 'Ringo'))
+
+    def check_html(self, widget, name, value, html='', attrs=None, **kwargs):
+        output = widget.render(name, value, attrs=attrs, **kwargs)
+        self.assertHTMLEqual(output, html)