Which of the following is NOT a common hardness test?

Tensile testing is primarily used to determine material strength properties, such as tensile strength, yield strength, and elongation, rather than hardness. In a tensile test, a sample material is pulled until it fails, and the resulting data provides insight into how the material behaves under tension, demonstrating its ductility and overall strength characteristics.

In contrast, Brinell, Rockwell, and Knoop tests are specifically designed to measure hardness, which is the resistance of a material to deformation or penetration. Each of these hardness tests employs different methods to assess how materials withstand indentations or impressions, providing valuable information about their mechanical properties.

Therefore, while the other tests focus on hardness assessment, tensile testing is distinct for evaluating the strength and ductility of materials, making it the option that does not belong to the common hardness testing methods.