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_checkboxinput.py

@@ -0,0 +1,87 @@
+from django.forms import CheckboxInput
+
+from .base import WidgetTest
+
+
+class CheckboxInputTest(WidgetTest):
+    widget = CheckboxInput()
+
+    def test_render_empty(self):
+        self.check_html(self.widget, 'is_cool', '', html='<input type="checkbox" name="is_cool" />')
+
+    def test_render_none(self):
+        self.check_html(self.widget, 'is_cool', None, html='<input type="checkbox" name="is_cool" />')
+
+    def test_render_false(self):
+        self.check_html(self.widget, 'is_cool', False, html='<input type="checkbox" name="is_cool" />')
+
+    def test_render_true(self):
+        self.check_html(
+            self.widget, 'is_cool', True,
+            html='<input checked="checked" type="checkbox" name="is_cool" />'
+        )
+
+    def test_render_value(self):
+        """
+        Using any value that's not in ('', None, False, True) will check the
+        checkbox and set the 'value' attribute.
+        """
+        self.check_html(
+            self.widget, 'is_cool', 'foo',
+            html='<input checked="checked" type="checkbox" name="is_cool" value="foo" />',
+        )
+
+    def test_render_int(self):
+        """
+        Integers are handled by value, not as booleans (#17114).
+        """
+        self.check_html(
+            self.widget, 'is_cool', 0,
+            html='<input checked="checked" type="checkbox" name="is_cool" value="0" />',
+        )
+        self.check_html(
+            self.widget, 'is_cool', 1,
+            html='<input checked="checked" type="checkbox" name="is_cool" value="1" />',
+        )
+
+    def test_render_check_test(self):
+        """
+        You can pass 'check_test' to the constructor. This is a callable that
+        takes the value and returns True if the box should be checked.
+        """
+        widget = CheckboxInput(check_test=lambda value: value.startswith('hello'))
+        self.check_html(widget, 'greeting', '', html=(
+            '<input type="checkbox" name="greeting" />'
+        ))
+        self.check_html(widget, 'greeting', 'hello', html=(
+            '<input checked="checked" type="checkbox" name="greeting" value="hello" />'
+        ))
+        self.check_html(widget, 'greeting', 'hello there', html=(
+            '<input checked="checked" type="checkbox" name="greeting" value="hello there" />'
+        ))
+        self.check_html(widget, 'greeting', 'hello & goodbye', html=(
+            '<input checked="checked" type="checkbox" name="greeting" value="hello &amp; goodbye" />'
+        ))
+
+    def test_render_check_exception(self):
+        """
+        Calling check_test() shouldn't swallow exceptions (#17888).
+        """
+        widget = CheckboxInput(
+            check_test=lambda value: value.startswith('hello'),
+        )
+
+        with self.assertRaises(AttributeError):
+            widget.render('greeting', True)
+
+    def test_value_from_datadict(self):
+        """
+        The CheckboxInput widget will return False if the key is not found in
+        the data dictionary (because HTML form submission doesn't send any
+        result for unchecked checkboxes).
+        """
+        self.assertFalse(self.widget.value_from_datadict({}, {}, 'testing'))
+
+    def test_value_from_datadict_string_int(self):
+        value = self.widget.value_from_datadict({'testing': '0'}, {}, 'testing')
+        self.assertEqual(value, True)