Fixed type and intended value of stubQuestions.get()

In getSkillQuestion() a call to stubQuestions.get() contained an argument
with an incompatible class. Session will be converted into String using
toString() but this is not what was intended to do here.

In saveQuestion() the CouchDB document ID was used, but the sessions
keyword should have been used instead.

src/test/java/de/thm/arsnova/dao/StubDatabaseDao.java

@@ -34,9 +34,9 @@ import de.thm.arsnova.entities.LoggedIn;
 import de.thm.arsnova.entities.Question;
 import de.thm.arsnova.entities.Session;
 import de.thm.arsnova.entities.SessionInfo;
+import de.thm.arsnova.entities.SortOrder;
 import de.thm.arsnova.entities.Statistics;
 import de.thm.arsnova.entities.User;
-import de.thm.arsnova.entities.SortOrder;
 import de.thm.arsnova.entities.transport.ImportExportSession;
 import de.thm.arsnova.exceptions.NoContentException;
 import de.thm.arsnova.exceptions.NotFoundException;
@@ -126,7 +126,7 @@ public class StubDatabaseDao implements IDatabaseDao {
 
 	@Override
 	public Question saveQuestion(Session session, Question question) {
-		List<Question> questions = stubQuestions.get(session.get_id());
+		List<Question> questions = stubQuestions.get(session.getKeyword());
 		questions.add(question);
 		stubQuestions.put(session.get_id(), questions);
 
@@ -141,11 +141,13 @@ public class StubDatabaseDao implements IDatabaseDao {
 
 	@Override
 	public List<Question> getSkillQuestions(User user, Session session) {
-		if (session == null)
+		if (session == null) {
 			throw new NotFoundException();
-		List<Question> questions = stubQuestions.get(session);
-		if (questions == null)
+		}
+		List<Question> questions = stubQuestions.get(session.getKeyword());
+		if (questions == null) {
 			throw new NoContentException();
+		}
 		return questions;
 	}
 
@@ -245,12 +247,12 @@ public class StubDatabaseDao implements IDatabaseDao {
 
 	@Override
 	public InterposedQuestion getInterposedQuestion(String questionId) {
-		return this.interposedQuestion;
+		return interposedQuestion;
 	}
 
 	@Override
 	public void markInterposedQuestionAsRead(InterposedQuestion question) {
-		this.interposedQuestion.setRead(true);
+		interposedQuestion.setRead(true);
 	}
 
 	@Override