TETO-principle means Test Early, Test Often. Test not too late, not too little and not for the wrong reasons.

TETO principle should be applied to every web design project as usability tests often provide crucial insights into significant problems and issues related to a given layout. Most design decisions are local and we can’t universally answer whether some layout is better than the other. Every web project should be analysed from its own specific point of view: considering requirements, stakeholders, budget etc..

Some important points to keep in mind:

• according to Steve Krug, testing one user is 100% better than testing none and testing one user early in the project is better than testing 50 near the end;
• accoring to Boehm’s first law, errors are most frequent during requirements and design activities and are the more expensive the later they are removed;
• testing is an iterative process: we design something, test it, fix it and then test it again. There might be problems which haven’t been found during the first round as users were practically blocked by other problems;
• usability tests always produce useful results. Either we’ll be pointed to the problems you have or we’ll be pointed to the absence of major design flaws which is in both cases a useful insight for your project;
• according to Weinberg’s law, a developer is unsuited to test his or her code. After working on a site for few weeks, we can’t observe it from a fresh perspective anymore.