better mds existence check

matlab/tests/check_mds.m

 classdef check_mds < matlab.unittest.fixtures.Fixture
   methods
     function setup(fixture)
-      fixture.assumeFalse(~exist('mdsdata','file'),'mdsdata not found - is mds on path?');
+      fixture.assumeFalse(~exist('mdsconnect','file'),'mdsdata not found - is mds on path?');
       % other environment checks here
     end
   end
-end
+end
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