i_900 fix junit for testing problem visibility by group

Fix ambiguity with using 'null' as argument to Problem.canView(obj).
Add unit tests for test testing problem visibility for a List<> of groups.

src/edu/csus/ecs/pc2/core/model/Problem.java

@@ -1946,7 +1946,7 @@ public void addGroup(Group group){
      */
     public boolean canView (Group group){
         boolean view = (groups.size() == 0);
-        if (group != null) {
+        if (!view && group != null) {
             for (Iterator<Group> iterator = groups.iterator(); iterator.hasNext();) {
                 Group g2 = iterator.next();
                 if (group.getDisplayName().equals(g2.getDisplayName())) {
@@ -1965,7 +1965,9 @@ public boolean canView (Group group){
      * @return true if any group can see the problem, false otherwise
      */
     public boolean canView(List<Group> wantedGroups) {
-        boolean view = (wantedGroups == null);
+        // If no specific groups are assigned to this problem or we're not interested
+        // in specific groups, then the problem is viewable.
+        boolean view = (groups.size() == 0 || wantedGroups == null);
 
         if(!view) {
             for(Group group : wantedGroups) {

test/edu/csus/ecs/pc2/core/model/ProblemTest.java

@@ -2,6 +2,8 @@
 package edu.csus.ecs.pc2.core.model;
 
 import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
 
 import edu.csus.ecs.pc2.core.Constants;
 import edu.csus.ecs.pc2.core.model.Problem.VALIDATOR_TYPE;
@@ -323,11 +325,20 @@ public void testAddGroup() throws Exception {
 
         Group group1 = groups[0];
 
+        ArrayList<Group> arrayOfGroup1 = new ArrayList<Group>();
+        arrayOfGroup1.add(group1);
+        ArrayList<Group> arrayOfGroup2 = new ArrayList<Group>();
+        arrayOfGroup2.add(groups[1]);
+
         assertTrue (lastProblem.isAllView());
         lastProblem.addGroup(group1);
 
         assertTrue (lastProblem.canView(group1));
-        assertFalse (lastProblem.canView(null));
+        assertFalse (lastProblem.canView((Group)null));
+        // a null wanted group list means "any group"
+        assertTrue (lastProblem.canView((List<Group>)null));
+        assertTrue (lastProblem.canView(arrayOfGroup1));
+        assertFalse (lastProblem.canView(arrayOfGroup2));
         assertFalse (lastProblem.canView(groups[1]));
 
         lastProblem.clearGroups();