"小规模试验厂" can be translated into English as "small-scale pilot plant" or "small-scale test plant."
"Small-scale" indicates the relatively small size or scope of the operation.
"Pilot plant" or "test plant" refers to a facility used for testing new processes, technologies, or products on a smaller scale before full-scale implementation.
Both translations are appropriate, depending on the context and the specific emphasis you want to place on the facility's purpose (e.g., whether it's more about testing processes or products).