Flexing and bending
Shoes, especially sneakers and sports shoes, need to support the foot but stay flexible. Flexing and bending the shoe repeatedly can detect weak spots such as insufficient glue or weak threads.
Whether the out-sole has been cured properly can be tested by pushing a fingernail into it. If the material rebounds, it’s a good indicator for proper curing.
Remarks: there are many other trials and quality control on-site tests for shoes to ensure symmetry, stability, fitting of insoles and many other points. The above-mentioned are the most important ones.