Increased test coverage to effectively 100%

Author: SamuelRoettgermann

src/main/java/de/tum/cit/aet/artemis/exam/domain/Exam.java

@@ -444,25 +444,25 @@ public void setExamArchivePath(String examArchivePath) {
     /**
      * check if students are allowed to see this exam
      *
-     * @return true, if students are allowed to see this exam, otherwise false, null if this cannot be determined
+     * @return true, if students are allowed to see this exam, otherwise false
      */
     @JsonIgnore
-    public Boolean isVisibleToStudents() throws IllegalStateException {
+    public boolean isVisibleToStudents() {
         if (visibleDate == null) {  // no visible date means the exam is configured wrongly and should not be visible!
-            throw new IllegalStateException("The exam " + this.title + " has no visible date set!");
+            return false;
         }
         return visibleDate.isBefore(ZonedDateTime.now());
     }
 
     /**
      * check if the exam has started
      *
-     * @return true, if the exam has started, otherwise false, null if this cannot be determined
+     * @return true, if the exam has started, otherwise false
      */
     @JsonIgnore
-    public Boolean isStarted() throws IllegalStateException {
+    public boolean isStarted() {
         if (startDate == null) {   // no start date means the exam is configured wrongly and we cannot answer the question!
-            throw new IllegalStateException("The exam " + this.title + " has no start date set!");
+            return false;
         }
         return startDate.isBefore(ZonedDateTime.now());
     }
@@ -473,7 +473,7 @@ public Boolean isStarted() throws IllegalStateException {
      * @return true, if the results are published, false if not published or not set!
      */
     @JsonIgnore
-    public Boolean resultsPublished() {
+    public boolean resultsPublished() {
         if (publishResultsDate == null) {
             return false;
         }

src/main/java/de/tum/cit/aet/artemis/exam/repository/ExamRepository.java

@@ -468,7 +468,7 @@ default Exam findWithExerciseGroupsAndExercisesAndDetailsByIdOrElseThrow(long ex
      * @return only the visible exams
      */
     default Set<Exam> filterVisibleExams(Set<Exam> exams) {
-        return exams.stream().filter(exam -> Boolean.TRUE.equals(exam.isVisibleToStudents())).collect(Collectors.toSet());
+        return exams.stream().filter(Exam::isVisibleToStudents).collect(Collectors.toSet());
     }
 
     /**