Since when? I worked in the chemical industry for 25 years, and never took any such test. Nor do I recall any "health warnings" on the various shop masks I have bought and used over the years.
Since 1998, when 29 CFR 1910.134 was promulgated. Subsection (e) recognizes, “Using a respirator may place a physiological burden on employees that varies with the type of respirator worn, the job and workplace conditions in which the respirator is used, and the medical status of the employee.” Subsection (e)(1) provides, “The employer shall provide a medical evaluation to determine the employee’s ability to use a respirator, before the employee is fit tested or required to use the respirator in the workplace.” The regulation goes on to specify the requirements of that evaluation.
If you are wondering whether a cloth mask, N95 mask, or dist mask is a “respirator,” the definition of “Filtering Facepiece (dist mask)” makes it clear that it is, as does the exception from the requirement for a written respiratory protection plan for “employees whose only use of respirators involves the voluntary use of filtering facepieces (dust masks).”
I’m not surprised that you were never required to undergo a medical evaluation. Routine disregard of OSHA seems to be the rule rather than the exception in many industries.