A target shim injected into a target process detects activity in a user interface and sets a target-busy status. A source shim injected into a source process detects the input being sent toward the target process to drive automated testing. The source shim determines that the target-busy status is set, and prevents the source process from sending the input until the status is clear. The target shim clears the status after confirming that a screen capture, accessibility test, localizability test, or other user interlace analysis operation has completed. Multiple source shims and/or multiple target shims may be present. Copies of a single automation shim component may be tailored for use as source shims or as target shims. Security processes and operating system processes may be listed to prevent interference from automation shims. User interface analysis module(s) may be loaded and/or unloaded “hot” while the target process is running.