const certificate = contract(Certificate);
certificate.setProvider(web3.currentProvider);
var certificateInstance =
certificate.at("0xfcdf59a5e2a43059d3d469f4aa31534d6c0d00b7");
return certificateInstance
    .ownerName() // state variable in the contract
    .then(function(_ownerName) {
      console.log(_ownerName);
      // getParam2 is the function with onlyOwner modifier
      return certificateInstance.getParam2({ from: owner });
    })
    .then(function(_value) {
      console.log(_value);
    });

...
return Certificate.at(certAddress);
}).then(function(instance){
    certInstance = instance;
    return certInstance.getParam2({from: owner});
}).then(function(_value){
    assert.equal(_value, "param2value", "modifier function returns correct value"
})