Heat shock and peel test are two of many tests of magnet wire. The following link tells you about the various test.
Simply put, you elongate your sample, wrap it around a mandrel, and place in an oven set at 20 Celsius higher than the thermal rating of the wire. If it is 155C wire then the oven is set at 175c. After a period of time, the sample is removed and there should not be visible cracks. Cracks generally are an indication of over cure.
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NEMA Magnet Wire Thermal Class Ratings File Format: PDF/Adobe Acrobat
This test is used to. evaluate the resistance to cracking of the film insulation. Some typical test conditions for copper magnet wire are: ...
www.spsx.com/uploadedFiles/News/White_Pa...al-class-ratings.pdf