Implement logic from JUnit tests

Question

I lost some Java code. I keep only several JUnit tests for hashing. I tried to implement this:

public interface HmacService {
    String hash(final String number);

    String getCheckhash(final String hash);
}
...
class HmacServiceImpl implements HmacService {

    public String hash(String number) {
        try {
            return Hashing.sha256().hashString(plainCardNumber, StandardCharsets.UTF_8).toString();
        } catch (Exception var3) {            
        }
    }

    public String getNonCreditCardSha1Hmac(String hash) {
        try {
          return Hashing.sha1().hashString(hash, StandardCharsets.UTF_8).toString();
        } catch (Exception var3) {            
        }
    }


   final class HashPair{
        String firstHash;
        String secondHash;

        public HashPair(String firstHash, String secondHash) {
            this.firstHash = firstHash;
            this.secondHash = secondHash;
        }
        
        // perform hash comparison here
    }
}

JUnit tests:

public HmacService.HashPair generateQuickHash(final String cardNum) {
    return cryptoService.generateHashPair(cardNum);
}

if(new HmacService.HashPair(oldHash, oldHash)) == null){
// some error message
}

Do you know how I can implement the code based on the JUnit tests?

Answer 1

This is testing HMAC-SHA-256 and there are countless Java implementations of it. The strange thing just is, that no signature is being passed - neither when hashing, nor when comparing the hashes. I don't think that the code has any real purpose alike this.

Answer 2

Depends on how strong your coverage of that part of the code was.

If it had high coverage, you can follow a TDD like approach doing Red-Green-Refactor cycles.

To start I would comment all failing tests but one (the simplest one) [first red] an then do the implementation to make it pass [first green].

Then uncomment the next test and implement again.

Rinse and repeat until all test are uncommented and passing.