SecureEntropyGeneratorTest.java

package com.example.bip39.entropy;

import static org.junit.jupiter.api.Assertions.assertArrayEquals;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;

import com.example.bip39.api.DefaultBip39Service;
import com.example.bip39.error.Bip39ErrorCode;
import com.example.bip39.error.Bip39Exception;
import com.example.bip39.util.Bip39Constants;
import java.util.Arrays;
import org.junit.jupiter.api.Test;

class SecureEntropyGeneratorTest {

  private static final String ZERO_ENTROPY_MNEMONIC =
      "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon"
          + " about";

  @Test
  void rejectsUnsupportedEntropyLengths() {
    SecureEntropyGenerator generator =
        new SecureEntropyGenerator(bytes -> Arrays.fill(bytes, (byte) 0));

    Bip39Exception exception =
        assertThrows(Bip39Exception.class, () -> generator.generateEntropy(12));

    assertEquals(Bip39ErrorCode.ERR_ENTROPY_LENGTH, exception.getErrorCode());
  }

  @Test
  void generatesAllAllowedEntropyLengths() {
    SecureEntropyGenerator generator =
        new SecureEntropyGenerator(bytes -> Arrays.fill(bytes, (byte) 0));

    for (int entropyLength : Bip39Constants.ALLOWED_ENTROPY_LENGTHS_BYTES) {
      assertEquals(entropyLength, generator.generateEntropy(entropyLength).length);
    }
  }

  @Test
  void generatesDeterministicEntropyWhenSourceIsInjected() {
    byte[] expectedEntropy = new byte[16];
    for (int index = 0; index < expectedEntropy.length; index++) {
      expectedEntropy[index] = (byte) (index + 1);
    }

    SecureEntropyGenerator generator =
        new SecureEntropyGenerator(
            bytes -> System.arraycopy(expectedEntropy, 0, bytes, 0, bytes.length));

    assertArrayEquals(expectedEntropy, generator.generateEntropy(16));
  }

  @Test
  void convertsGeneratedEntropyThroughBip39ServiceUsingThinAdapter() {
    SecureEntropyGenerator generator =
        new SecureEntropyGenerator(bytes -> Arrays.fill(bytes, (byte) 0));

    assertEquals(ZERO_ENTROPY_MNEMONIC, generator.generateMnemonic(16, new DefaultBip39Service()));
  }
}