In reply to rajan passionate:
Make a faster clk in the TB , say 3x SCL
But, in I2C , data toggling takes place when SCL is low, except for start condition.
You enable your assertions after start is detected , to check data toggling when SCL is low.
Detect start like -
@(negedge iic_if_i.Sda);
if(iic_if_i.Scl) begin
start_detected = 1;