add multiple correct values check for Dropdown problems

common/lib/capa/capa/capa_problem.py

@@ -245,6 +245,22 @@ class LoncapaProblem(object):
         This translation takes in the new format and synthesizes the old option= attribute
         so all downstream logic works unchanged with the new <option> tag format.
         """
+        def is_optioninput_valid(optioninput):
+            """
+            Verifies if a given optioninput xml is valid or not.
+
+            A given optioninput(Dropdown) problem is invalid if it has more than one correct answer.
+
+            Argument:
+                optioninput: dropdown specification tree
+            Returns:
+                boolean: signifying if the optioninput is valid or not.
+            """
+            correct_options = [
+                option.get('correct').upper() == 'TRUE' for option in optioninput.findall('./option')
+            ]
+            return correct_options.count(True) in (0, 1)
+
         additionals = tree.xpath('//stringresponse/additional_answer')
         for additional in additionals:
             answer = additional.get('answer')
@@ -252,8 +268,9 @@ class LoncapaProblem(object):
             if not answer and text:  # trigger of old->new conversion
                 additional.set('answer', text)
                 additional.text = ''
-
         for optioninput in tree.xpath('//optioninput'):
+            if not is_optioninput_valid(optioninput):
+                raise responsetypes.LoncapaProblemError("Dropdown questions can only have one correct answer.")
             correct_option = None
             child_options = []
             for option_element in optioninput.findall('./option'):

common/lib/capa/capa/tests/test_capa_problem.py

@@ -12,6 +12,7 @@ from lxml import etree
 from markupsafe import Markup
 from mock import patch
 
+from capa.responsetypes import LoncapaProblemError
 from capa.tests.helpers import new_loncapa_problem
 from openedx.core.djangolib.markup import HTML
 
@@ -460,6 +461,37 @@ class CAPAProblemTest(unittest.TestCase):
         self.assert_question_tag(question1, question2, tag='label', label_attr=False)
         self.assert_question_tag(question1, question2, tag='p', label_attr=True)
 
+    def test_optionresponse_xml_compatibility(self):
+        """
+        Verify that an optionresponse problem with multiple correct answers is not instantiated.
+
+        Scenario:
+        Given an optionresponse/Dropdown problem
+        If there are multiple correct answers
+        Then the problem is not instantiated
+        And Loncapa problem error exception is raised
+        If the problem is corrected by including only one correct answer
+        Then the problem is created successfully
+        """
+        xml = """
+        <problem>
+            <optionresponse>
+              <p>You can use this template as a guide to the simple editor markdown and OLX markup to use for dropdown problems. Edit this component to replace this template with your own assessment.</p>
+            <label>Add the question text, or prompt, here. This text is required.</label>
+            <description>You can add an optional tip or note related to the prompt like this. </description>
+            <optioninput>
+                <option correct="False">an incorrect answer</option>
+                <option correct="True">the correct answer</option>
+                <option correct="{correctness}">an incorrect answer</option>
+              </optioninput>
+            </optionresponse>
+        </problem>
+        """
+        with self.assertRaises(LoncapaProblemError):
+            new_loncapa_problem(xml.format(correctness=True))
+        problem = new_loncapa_problem(xml.format(correctness=False))
+        self.assertIsNotNone(problem)
+
 
 @ddt.ddt
 class CAPAMultiInputProblemTest(unittest.TestCase):

common/lib/xmodule/xmodule/capa_module.py

@@ -344,7 +344,7 @@ class ProblemBlock(
 
     def max_score(self):
         """
-        Return the problem's max score
+        Return the problem's max score if problem is instantiated successfully, else return max score of 0.
         """
         from capa.capa_problem import LoncapaProblem, LoncapaSystem
         capa_system = LoncapaSystem(
@@ -363,16 +363,22 @@ class ProblemBlock(
             xqueue=None,
             matlab_api_key=None,
         )
-        lcp = LoncapaProblem(
-            problem_text=self.data,
-            id=self.location.html_id(),
-            capa_system=capa_system,
-            capa_module=self,
-            state={},
-            seed=1,
-            minimal_init=True,
-        )
-        return lcp.get_max_score()
+        try:
+            lcp = LoncapaProblem(
+                problem_text=self.data,
+                id=self.location.html_id(),
+                capa_system=capa_system,
+                capa_module=self,
+                state={},
+                seed=1,
+                minimal_init=True,
+            )
+        except responsetypes.LoncapaProblemError:
+            log.exception(u"LcpFatalError for block {} while getting max score".format(str(self.location)))
+            maximum_score = 0
+        else:
+            maximum_score = lcp.get_max_score()
+        return maximum_score
 
     def generate_report_data(self, user_state_iterator, limit_responses=None):
         """

common/lib/xmodule/xmodule/tests/test_capa_module.py

@@ -2871,6 +2871,27 @@ class ProblemBlockXMLTest(unittest.TestCase):
         with self.assertRaises(etree.XMLSyntaxError):
             self._create_descriptor(sample_invalid_xml, name="Invalid XML")
 
+    def test_invalid_dropdown_xml(self):
+        """
+        Verify the capa problem cannot be created from dropdown xml with multiple correct answers.
+        """
+        problem_xml = textwrap.dedent("""
+        <problem>
+            <optionresponse>
+              <p>You can use this template as a guide to the simple editor markdown and OLX markup to use for dropdown problems. Edit this component to replace this template with your own assessment.</p>
+            <label>Add the question text, or prompt, here. This text is required.</label>
+            <description>You can add an optional tip or note related to the prompt like this. </description>
+            <optioninput>
+                <option correct="False">an incorrect answer</option>
+                <option correct="True">the correct answer</option>
+                <option correct="True">an incorrect answer</option>
+              </optioninput>
+            </optionresponse>
+        </problem>
+        """)
+        with self.assertRaises(Exception):
+            CapaFactory.create(xml=problem_xml)
+
 
 class ComplexEncoderTest(unittest.TestCase):