Support encoding and decoding of NegativeUNL pseudo-transactions (#89)

* Support encoding and decoding of NegativeUNL pseudo-transactions

packages/ripple-binary-codec/test/pseudo-transaction.test.js

@@ -0,0 +1,37 @@
+const { encode, decode } = require('../dist')
+
+let json = {
+    "Account": "rrrrrrrrrrrrrrrrrrrrrhoLvTp",
+    "Sequence": 0,
+    "Fee": "0",
+    "SigningPubKey": "",
+    "Signature": ""
+}
+
+let json_blank_acct = {
+    "Account": "",
+    "Sequence": 0,
+    "Fee": "0",
+    "SigningPubKey": "",
+    "Signature": ""
+}
+
+let binary = "24000000006840000000000000007300760081140000000000000000000000000000000000000000"
+
+describe("Can encode Pseudo Transactions", () => {
+    test("Correctly encodes Pseudo Transaciton", () => {
+        expect(encode(json)).toEqual(binary);
+    })
+
+    test("Can decode account objects", () => {
+        expect(decode(encode(json))).toEqual(json);
+    })
+
+    test("Blank AccountID is ACCOUNT_ZERO", () => {
+        expect(encode(json_blank_acct)).toEqual(binary)
+    })
+
+    test("Decodes Blank AccountID", () => {
+        expect(decode(encode(json_blank_acct))).toEqual(json);
+    })
+})