define Wallet class (#1509)

* define Wallet class
- Wallet class is a utility for deriving a wallet composed of a keypair (publicKey/privateKey).
- A wallet can be derived from either a seed, mnemnoic, or entropy (array of random numbers).
- It provides functionality to sign/verify transactions offline.

test/wallet/verifyTransaction/index.ts

@@ -0,0 +1,46 @@
+import assert from 'assert-diff'
+import {TestSuite} from '../../utils'
+import Wallet from 'ripple-api/Wallet'
+
+const publicKey =
+  '030E58CDD076E798C84755590AAF6237CA8FAE821070A59F648B517A30DC6F589D'
+const privateKey =
+  '00141BA006D3363D2FB2785E8DF4E44D3A49908780CB4FB51F6D217C08C021429F'
+const prepared = {
+  signedTransaction:
+    '1200002400000001614000000001312D0068400000000000000C7321030E58CDD076E798C84755590AAF6237CA8FAE821070A59F648B517A30DC6F589D74473045022100CAF99A63B241F5F62B456C68A593D2835397101533BB5D0C4DC17362AC22046F022016A2CA2CF56E777B10E43B56541A4C2FB553E7E298CDD39F7A8A844DA491E51D81142AF1861DEC1316AEEC995C94FF9E2165B1B784608314FDB08D07AAA0EB711793A3027304D688E10C3648',
+  id: '30D9ECA2A7FB568C5A8607E5850D9567572A9E7C6094C26BEFD4DC4C2CF2657A'
+}
+
+/**
+ * Every test suite exports their tests in the default object.
+ * - Check out the "TestSuite" type for documentation on the interface.
+ * - Check out "test/api/index.ts" for more information about the test runner.
+ */
+export default <TestSuite>{
+  'verify transaction offline when a signed transaction is valid': async (api) => {
+    // GIVEN a transaction that has been signed by the same wallet
+    const wallet = new Wallet(publicKey, privateKey)
+
+    // WHEN verifying a signed transaction
+    const isVerified: boolean = wallet.verifyTransaction(prepared.signedTransaction)
+
+    // THEN we get a valid response
+    assert.equal(isVerified, true)
+  },
+
+  "verify transaction offline when signed transaction isn't valid": async (api) => {
+    // GIVEN a transaction that has been signed by a different wallet
+    const diffPublicKey =
+      '02F89EAEC7667B30F33D0687BBA86C3FE2A08CCA40A9186C5BDE2DAA6FA97A37D8'
+    const diffPrivateKey =
+      '00ACCD3309DB14D1A4FC9B1DAE608031F4408C85C73EE05E035B7DC8B25840107A'
+    const wallet = new Wallet(diffPublicKey, diffPrivateKey)
+
+    // WHEN verifying a signed transaction
+    const isVerified: boolean = wallet.verifyTransaction(prepared.signedTransaction)
+
+    // THEN we get an invalid response
+    assert.equal(isVerified, false)
+  },
+}