I'm personally of the opinion that this comprises a large portion (>60%) of the value of unit tests. Unit testable code tends to not have many of the side effe

I'm personally of the opinion that this comprises a large portion (>60%) of the value of unit tests. Unit testable code tends to not have many of the side effects / global variables / nasty state that make nasty bugs, so this alone tends to drive down the number and severity of bugs. The testing itself is icing on the cake.