Design can also be detected and tested. Archeologists, forensic scientists cryptographers etc detect design all the time .
Do you know what “archaeology” is?
Archaeology is the the study of human history, through what people build/construct (eg cities, towns, both public and private buildings, roads, bridges, tombs, etc) or what they make (artefacts, like art works, minted coins, pottery, combs, tools, weapons, etc, all “man-made”.
So of course, archaeology involved designs, because they all involved discoveries of man-made construction or man-made objects.
Do you understand what is cryptology?
Cryptography is also “man-made” writing, reading, encrypting or deciphering codes. They are written, read, breaking all by people, humans.
As to forensic science, it is the study of how people died, whether it by natural causes (which could be of old age or diseases) or by killing (murders, through gunshot, blows). It is the later (the killing), is the main reasons that forensic science is used to gather evidences against perpetrators for some crimes committed, which are to be used for court of law. Forensic science is used to determine how crimes were committed, by gathering evidences.
All these have nothing too do with the Designer of Intelligent Design, whether that “designer” or “designers” be god, alien, or some other mythological beings.
No invisible and all-powerful Designer, Creator or God involved in town-planning, architecture, sculptures, making coins, tools or weapons made (archaeology), nor are they involved encrypting or deciphering hidden codes (cryptology), nor solving crimes through finding evidences (solving).
What does any of these (archaeology, cryptology or forensic science) have to do with Intelligent Design or with Creationism?
Again, you are making silly comparisons of the real world that involved human activities to that of the supernatural, which are ID.