They take the shovel and dig a sample. Eric and T take that soil sample and feel the soil, even smell the soil. T can't make a ball with it, it just falls apart. This is a sandy soil. By comparison the soil behind the rock wall has a whole different character. One can actually make a solid clump in their hands, and it stays together. It has a lot more clay and silt. It even has a different smell. People can often make that assessment just by touch, feel and smell. From that one can get a sense of how that soil will perform.
Next they perform a perk test to see how quickly water infiltrates through the soil. To do this dig a hole, fill that hole with water, determine how much water has been added, then let the hole drain for 15 minutes and refill. From that point you start measuring the amount of time it takes the water to infiltrate. This test is important and tells a lot about drainage and the type of soil you're working with. T considers the ideal percolation rate for good horticultural soil to be a minimum of an inch per hour.