Yes, this is certainly true to a (I think) minimal extend. Why? Because improving the time you spend on testing is something that is essentially hard to do -- and only a meta-information, anyway.
An example: A quality assessment of your code tells you that your methods are too long. This gives you a concrete task to do: You simply split all too-long methods. However, with testing time, this is not so: Increasing the effort spent on testing is something you cannot "just do" without a sensible plan. If you want to increase this metric, you have to start to think what is wrong with your current test strategy (maybe nothing's wrong at all), and come up with an action plan of how to do.
If you're that far in the game already, I think this metric has done what it can do. Plus, you'll likely see an increase in the metric. Which is justified.
Coming up with (critical) test efforts in the wild is our task now.
An example: A quality assessment of your code tells you that your methods are too long. This gives you a concrete task to do: You simply split all too-long methods. However, with testing time, this is not so: Increasing the effort spent on testing is something you cannot "just do" without a sensible plan. If you want to increase this metric, you have to start to think what is wrong with your current test strategy (maybe nothing's wrong at all), and come up with an action plan of how to do.
If you're that far in the game already, I think this metric has done what it can do. Plus, you'll likely see an increase in the metric. Which is justified.
Coming up with (critical) test efforts in the wild is our task now.