ELMER is a visible imager and spectrograph for the GTC. ELMER is currently in the final stage of testing (at the PO in La Laguna, Tenerife) previous to be shipped to the Observatorio del Roque de los Muchachos in the island of La Palma, where the GTC telescope is being integrated. ELMER Optics has been exhaustively tested at different steps, from the blanks to the final assemblies in order to guarantee the required performance. In this contribution, we will describe the tests done to the different optical components until now. Blank testing, WFE Image quality and transmission tests have been carried out for most of the components. A brief review of some of these tests is included in the following sections as well as a list of references where the test assemblies and the results are discussed in detail.