Add check if connection request to same or diff host.

Author: guzman-raphael

+dj/conn.m

@@ -33,9 +33,16 @@
 
 if isa(CONN, 'dj.Connection') && ~reset
     if nargin>0
-        warning(sprintf(['Connection already instantiated.\n' ...
-            'Will use existing connection to "' CONN.host '".\n' ...
-            'To reconnect, set reset to true']));
+        if strcmp(CONN.host,host)
+            warning('DataJoint:Connection:AlreadyInstantiated', sprintf([...
+                'Connection already instantiated.\n' ...
+                'Will use existing connection to "' CONN.host '".\n' ...
+                'To reconnect, set reset to true']));
+        else
+            error('DataJoint:Connection:AlreadyInstantiated', sprintf([...
+                'Connection already instantiated to "' CONN.host '".\n' ...
+                'To reconnect, set reset to true']));
+        end
     end
 else
     % invoke setupDJ

+tests/TestConnection.m

@@ -10,12 +10,25 @@ function testConnection(testCase)
                 testCase.CONN_INFO.password,'',true).isConnected);
         end
         function testConnectionExists(testCase)
-            % testConnectionExists tests that will not fail if connection open.
+            % testConnectionExists tests that will not fail if connection open
+            % to the same host.
             % Fix https://github.com/datajoint/datajoint-matlab/issues/160
             st = dbstack;
             disp(['---------------' st(1).name '---------------']);
             dj.conn(testCase.CONN_INFO.host, '', '', '', '', true)
             dj.conn(testCase.CONN_INFO.host, '', '', '', '', true)
         end
+        function testConnectionDiffHost(testCase)
+            % testConnectionDiffHost tests that will fail if connection open
+            % to a different host.
+            % Fix https://github.com/datajoint/datajoint-matlab/issues/160
+            st = dbstack;
+            disp(['---------------' st(1).name '---------------']);
+            dj.conn(testCase.CONN_INFO.host, '', '', '', '', true)
+            
+            testCase.verifyError(@() dj.conn(...
+                'anything', '', '', '', '', true), ...
+                'DataJoint:Connection:AlreadyInstantiated');
+        end
     end
 end