Turn on your Multimeter and select diode port in the meter. Now connect red wire to the positive point of diode and black wire to the negative point of diode. And check the value if the meter shows 000 as shown in picture then the diode is damaged . Or if it shows some value like 678,774 or others it means the diode is ok .
How to identify the positive point of diode?
In the upper side of diode u will see a dark line which shows this point is positive and other is negative.

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