feat: test coverage increase in ed25519.ts (#815)

Resolves #136 
Completely covers the `ed25519.ts` file with 100% coverage.

| File Name          | Statements | Branches | Functions | Lines  |
|--------------------|------------|----------|-----------|--------|
| **Before:**        |            |          |           |        |
| All files          |   99.05    |   97.55  |   96.04   |  99.05 |
| ed25519.ts         |   93.1     |   88.88  |   83.33   |  93.1  |
| **After:**         |            |          |           |        |
| All files          |   99.09    |   97.6   |   96.25   |  99.09 |
| ed25519.ts         |   100      |   100    |   100     |  100   |

tests/jose/jws/general.spec.ts

@@ -1,13 +1,18 @@
+import chai from 'chai';
 import chaiAsPromised from 'chai-as-promised';
-import chai, { expect } from 'chai';
+import { expect } from 'chai';
+import sinon from 'sinon';
+import { UniversalResolver } from '@web5/dids';
 
+import { ed25519 } from '../../../src/jose/algorithms/signing/ed25519.js';
+import { Encoder } from '../../../src/utils/encoder.js';
 import { GeneralJwsBuilder } from '../../../src/jose/jws/general/builder.js';
 import { GeneralJwsVerifier } from '../../../src/jose/jws/general/verifier.js';
 import { Jws } from '../../../src/utils/jws.js';
 import { PrivateKeySigner } from '../../../src/index.js';
 import { signatureAlgorithms } from '../../../src/jose/algorithms/signing/signature-algorithms.js';
-import sinon from 'sinon';
-import { UniversalResolver } from '@web5/dids';
+import { DwnError, DwnErrorCode } from '../../../src/core/dwn-error.js';
+
 
 const { Ed25519, secp256k1 } = signatureAlgorithms;
 const secp256r1 = signatureAlgorithms['P-256'];
@@ -124,6 +129,34 @@ describe('General JWS Sign/Verify', () => {
     expect(verificationResult.signers).to.include('did:jank:alice');
   });
 
+  it('should throw an error for invalid Ed25519 JWK', async () => {
+    const invalidJwk = {
+      kty : 'RSA', // Invalid key type
+      crv : 'Ed25519',
+      d   : 'invalid-private-key'
+    };
+
+    const content = new TextEncoder().encode('anyPayloadValue');
+
+    try {
+      await ed25519.sign(content, invalidJwk as any);
+      expect.fail('Expected an error to be thrown');
+    } catch (error) {
+      expect(error).to.be.instanceOf(DwnError);
+      expect((error as DwnError).code).to.equal(DwnErrorCode.Ed25519InvalidJwk);
+      expect((error as DwnError).message).to.include('invalid jwk. kty MUST be OKP. crv MUST be Ed25519');
+    }
+  });
+
+  it('should convert public key bytes to JWK', async () => {
+    const { publicJwk } = await ed25519.generateKeyPair();
+    const publicKeyBytes = Encoder.base64UrlToBytes(publicJwk.x);
+
+    const convertedJwk = await ed25519.publicKeyToJwk(publicKeyBytes);
+
+    expect(convertedJwk).to.deep.equal(publicJwk);
+  });
+
   it('should support multiple signatures using different key types', async () => {
     const secp256k1Keys = await secp256k1.generateKeyPair();
     const ed25519Keys = await Ed25519.generateKeyPair();