You can get some erroneous test results if you don't pay careful attention to test specification requirements and laboratory testing details.
A tensile test is performed to determine the strength of a metal under predictable loading conditions. Tensile test results show how materials should perform in actual service, as designed. In other words, the tensile test is a good predictor of how the part will react under real life loading. With most metals, thermal processing can alter those properties greatly so proper testing can assure that the part was processed correctly. Hardness testing using Rockwell and Brinell methods is also useful, and often is used in conjunction with a tensile test to assure quality. ASTM standards provide procedures of testing metals (see sidebar).