There's something satisfying about seeing your tests pass after spending days building, breaking, fixing, and rebuilding the same program.
Over the past week, I worked on a simple counter program with Anchor. At first glance, it doesn't look like much, it just initializes a counter and increments it. But behind those few lines of code are some important lessons about Solana programs, account validation, and why good tests matter.
The first thing that stood out to me was the Initialize accounts struct. Coming from a more traditional development background, it took me a while to appreciate that most of the "magic" in Anchor happens before your instruction logic even runs. The accounts struct defines exactly which accounts are needed, who owns them, who pays for them, and what constraints must be satisfied. Once I understood that, the rest of the program started making a lot more sense.
The initialize handler itself is surprisingly short. That's because ctx.accounts gives you direct access to all the validated accounts you declared earlier. Instead of writing lots of validation logic yourself, Anchor handles it for you. All the handler needs to do is set the initial value of the counter.
The increment instruction taught me another valuable lesson. By adding an account constraint that checks the authority, I learned that security doesn't always belong inside the function body. Anchor verifies those constraints before the instruction executes, preventing unauthorized users from incrementing someone else's counter. That small addition made me appreciate how much safer programs can become when validation is built into the framework.
Writing the tests was where everything really clicked.
The happy-path test confirmed that a newly initialized counter starts with the expected value and increments correctly. If that test ever fails, it means the program's core functionality is broken.
The unauthorized increment test became my favorite. It attempts to increment a counter using the wrong wallet and expects the transaction to fail. If that test unexpectedly passes, it means anyone could modify someone else's counter, a serious security flaw. That single test gave me much more confidence in the program.
One of the most eye-opening exercises was intentionally introducing bugs into the code. For one experiment, I changed:
counter.count += 1;
to
counter.count += 2;
I expected everything to compile, and it did. But my tests immediately failed because the final counter value was no longer what the assertions expected.
That moment reinforced an important lesson for me: passing compilation doesn't mean your program is correct. Tests are what prove your code behaves the way you intended.
This project may be a simple counter, but it taught me much more than incrementing numbers. It helped me understand how Anchor validates accounts, how instruction handlers stay clean because of those validations, and why writing failure-path tests is just as important as testing successful transactions.
If I had another week to improve this project, I'd explore custom error codes, event logging, Program Derived Addresses (PDAs), and more advanced account relationships to better understand how real-world Solana programs are structured.
Small projects often teach the biggest lessons.
Top comments (0)