A test circuit for testing a monitoring circuit includes: a ramp generator configured to generate a ramp signal in response to an activated first control signal; a counter configured to count pulses of a clock signal in response to the activated first control signal; at least one register configured to store an output value of the counter based on a change in at least one output signal generated by the monitoring circuit in response to the ramp signal in a test mode; and a controller configured to generate the first control signal and verify the monitoring circuit based on a ratio of a value stored in the at least one register to a duration during which the first control signal is activated.