What location is NOT suitable for conducting a usability test?

The primary goal of usability testing is to observe and record user behavior while interacting with the system. A location where user actions cannot be seen or recorded (option A) completely undermines the test's purpose and is therefore not suitable.

While options B, C, and D are not ideal in all cases, they can still be valid settings depending on the context. Testing in a user’s natural environment (B) increases ecological validity. Remote testing via video link (C) is widely accepted. Testing in a public setting (D) can be useful for mobile apps or services intended for real-world use.