How to use the fabric-common.Signer function in fabric-common

.then((dsID) => {
			t.equal(dsID._certificate, TEST_CERT_PEM, 'Identity class function tests: deserialized certificate');
			t.equal(dsID._publicKey.isPrivate(), false, 'Identity class function tests: deserialized public key');
			t.equal(dsID._publicKey._key.pubKeyHex, '0452a75e1ee105da7ab3d389fda69d8a04f5cf65b305b49cec7cdbdeb91a585cf87bef5a96aa9683d96bbabfe60d8cc6f5db9d0bc8c58d56bb28887ed81c6005ac', 'Identity class function tests: deserialized public key ecparam check');

			// manually construct a key based on the saved privKeyHex and pubKeyHex
			const f = KEYUTIL.getKey(TEST_KEY_PRIVATE_PEM);
			const testKey = new ecdsaKey(f);
			pubKey = testKey.getPublicKey();

			const signer = new Signer(cryptoUtils, testKey);
			t.equal(signer.getPublicKey().isPrivate(), false, 'Test Signer class getPublicKey() method');

			const signingID = new SigningIdentity(TEST_KEY_PRIVATE_CERT_PEM, pubKey, mspImpl.getId(), cryptoUtils, signer);

			t.throws(
				() => {
					signingID.sign(TEST_MSG, {hashFunction: 'not_a_function'});
				},
				/The "hashFunction" field must be a function/,
				'Test invalid hashFunction parameter for the sign() method'
			);

			const sig = signingID.sign(TEST_MSG);
			t.equal(cryptoUtils.verify(pubKey, sig, TEST_MSG), true, 'Test SigningIdentity sign() method');
			t.equal(signingID.verify(TEST_MSG, sig), true, 'Test Identity verify() method');
			t.end();

}).then((pubKey) => {
			t.pass('Successfully imported public key from the resulting enrollment certificate');

			const cryptoSuite = caService.getCryptoSuite();
			const id = ORGS[userOrg].mspid;

			signingIdentity = new SigningIdentity(eResult.certificate, pubKey, id, cryptoSuite, new Signer(cryptoSuite, eResult.key));
			return timeOutTest(signingIdentity, t);
		}, (err) => {
			t.fail('Failed to import the public key from the enrollment certificate. ' + err.stack ? err.stack : err);

() => {
			new Signer('blah');
		},
		/Missing required parameter "key" for private key/,

throw new Error('Invalid parameter. Must have a valid private key.');
		}
		if (typeof certificate === 'undefined' || certificate === null || certificate === '') {
			throw new Error('Invalid parameter. Must have a valid certificate.');
		}
		if (typeof mspid === 'undefined' || mspid === null || mspid === '') {
			throw new Error('Invalid parameter. Must have a valid mspid.');
		}
		let crypto_suite = this.getCryptoSuite();
		if (!crypto_suite) {
			crypto_suite = BaseClient.newCryptoSuite();
		}
		const key = await crypto_suite.createKeyFromRaw(private_key);
		const public_key = await crypto_suite.createKeyFromRaw(certificate);

		this._adminSigningIdentity = new SigningIdentity(certificate, public_key, mspid, crypto_suite, new Signer(crypto_suite, key));
	}