I feel there are two issues here. The first is that you didn't realize in advance that your original design may not be the best approach. Had you known this in advance, you may have been chosen to do a quick throw-away prototype or two, to explore the possible design options and to assess which is the most promising way to follow. In prototyping, you need not write production quality code and need not unit test every nook and cranny, as the point is to learn, not the code you wrote. So you can go faster.

Now, realizing that you need prototyping and experiments rather than starting the development of production code right away, is not always easy, and not even always possible. Armed with the knowledge just gained, you may be able to recognize the need for prototyping next time. Or may not. But at least you know now that this option is to be considered. And this in itself is important knowledge.

The other issue is with your perception. We all make mistakes, and it is so easy to see in retrospect what we should have done differently. This is just the way we learn. Write down your investment into unit tests as the price of learning that prototyping may be important, and get over it. Just try to do it better next time :-)

I feel there are two issues here. The first is that you didn't realize in advance that your original design may not be the best approach. Had you known this in advance, you may have chosen to develop a quick throw-away prototype or two, to explore the possible design options and to assess which is the most promising way to follow. In prototyping, you need not write production quality code and need not unit test every nook and cranny (or at all), as your sole focus is on learning, not on polishing the code.

Now, realizing that you need prototyping and experiments rather than starting the development of production code right away, is not always easy, and not even always possible. Armed with the knowledge just gained, you may be able to recognize the need for prototyping next time. Or may not. But at least you know now that this option is to be considered. And this in itself is important knowledge.

The other issue is IMHO with your perception. We all make mistakes, and it is so easy to see in retrospect what we should have done differently. This is just the way we learn. Write down your investment into unit tests as the price of learning that prototyping may be important, and get over it. Just strive not to make the same mistake twice :-)