Fix TrueFalse responses with single answers.

common/lib/capa/capa/responsetypes.py

@@ -1323,9 +1323,11 @@ class TrueFalseResponse(MultipleChoiceResponse):
 
     def get_score(self, student_answers):
         correct = set(self.correct_choices)
-        answers = set(student_answers.get(self.answer_id, []))
+        answers = student_answers.get(self.answer_id, [])
+        if not isinstance(answers, list):
+            answers = [answers]
 
-        if correct == answers:
+        if correct == set(answers):
             return CorrectMap(self.answer_id, 'correct')
 
         return CorrectMap(self.answer_id, 'incorrect')

common/lib/capa/capa/tests/test_responsetypes.py

@@ -151,6 +151,11 @@ class TrueFalseResponseTest(ResponseTest):
         self.assert_grade(problem, 'choice_foil_4', 'incorrect')
         self.assert_grade(problem, 'not_a_choice', 'incorrect')
 
+    def test_single_correct_response(self):
+        problem = self.build_problem(choices=[True, False])
+        self.assert_grade(problem, 'choice_0', 'correct')
+        self.assert_grade(problem, ['choice_0'], 'correct')
+
 
 class ImageResponseTest(ResponseTest):
     xml_factory_class = ImageResponseXMLFactory