Katana swords were tested through a process known as tameshigiri, which translates to "test cutting" in English. Tameshigiri was a critical step in the production of a katana to ensure its quality, sharpness, and cutting ability. The testing process involved slicing through various targets to assess the sword's performance.

Here is an overview of the tameshigiri process:

1. Cutting Targets: Traditional tameshigiri involved cutting through various materials, typically rolled or soaked straw mats called tatami omote. These mats were bound tightly together to create a dense target that simulated the resistance of human flesh and bone. Other materials like bamboo or thin metal sheets might also be used as secondary targets.
2. Testing Techniques: The swordsmith or a skilled practitioner would perform different cutting techniques to evaluate the sword's performance. This included diagonal cuts, horizontal cuts, and thrusting motions. The purpose was to assess the sword's sharpness, edge alignment, balance, and overall cutting efficiency.
3. Evaluation: After each cut, the practitioner would examine the cut's quality and assess the sword's performance based on factors like cleanness, depth, and smoothness of the cut. The sword's ability to slice through the target cleanly with minimal effort was considered an indication of its quality.
4. Honing and Refinement: If any issues were identified during testing, the sword would be further refined and honed to improve its performance. This might involve adjusting the edge geometry, heat treatment, or other aspects of the blade to enhance its cutting ability.

Tameshigiri was not only a quality control measure but also a way to demonstrate the sword's effectiveness and inspire confidence in its performance. Skilled practitioners would conduct the testing, often those with expertise in martial arts or experienced swordsmen.

It's worth noting that modern tameshigiri is still practiced today as a way to appreciate the traditional art of sword cutting and to showcase the quality and craftsmanship of Japanese swords.