### Question:
SigningKey { @Override public String toString() { return Encoder.HEX.encode(seed); } SigningKey(byte[] seed);  SigningKey();  SigningKey(String seed, Encoder encoder); VerifyKey getVerifyKey(); byte[] sign(byte[] message); String sign(String message, Encoder encoder); byte[] toBytes(); @Override String toString();  }### Answer:
@Test public void testCreateHexValidKey() throws Exception { try { new SigningKey(SIGN_PRIVATE, HEX).toString(); } catch (Exception e) { e.printStackTrace(); fail("Should return a valid key size"); } }
@Test public void testSerializesToHex() throws Exception { try { SigningKey key = new SigningKey(SIGN_PRIVATE, HEX); assertEquals("Correct sign key expected", SIGN_PRIVATE, key.toString()); } catch (Exception e) { fail("Should return a valid key size"); } }