The "stretch test" is very important for comfort & getting a good fit. To get an accurate read, fold the fabric & use the folded edge - at least 6" (15.24cm) from selvage & cut edge - to test against the scale. This simple test will ensure that the fabric you would like to use has sufficient elasticity for the pattern before making the purchase.
The following photos show pins for demonstration purposes, while in store just holding the fabric to the scale & stretching as indicated is very quick & easy.
When looking at the fabric check the "curl factor" .
Certain stretch fabrics tend to curl, as shown in the photo on the right hand side & can be seen on the cut edge right on the bolt.
This adds a degree of difficulty to the sewing project in placing pieces, cutting accuracy & the actual sewing.
Avoid the following types of fabric: