A testing method is disclosed. The testing method includes: providing a mixture solution of a gelling agent and a microbe to a gelling device; solidifying the mixture solution to form a solid thin film in which the microbe is immobilized; supplying a bioactive agent to the solid thin film and allowing the bioactive agent to diffuse into the solid thin film; and imaging the individual responses of the single microbial cells to the bioactive agent, and determining the minimum inhibitory concentration (MIC) of the bioactive agent based on the analysis of the images to obtain AST results.