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One of the steps for developing a cure in the "Lab challenge" is to test it. To do it a card of the cure color must be put on the test space and one disease cube of the color can be removed from any city.
Is it allowed to test a single cure multiple times? This would make it possible to treat the disease in a far away city (and reducing the number of city cards available for the cure).
Each cure can only be tested once, because there is only one card supposed to be on each field (although this is never actually stated in the rules). Note that the test card stays in place if the sequence card is exchanged within the color.