Improve test coverage

src/js/ripple/currency.js

@@ -52,7 +52,7 @@ Currency.prototype.equals = function (d) {
 // this._value = NaN on error.
 Currency.prototype.parse_json = function (j) {
   if (j instanceof Currency) {
-    this._value = j;
+    j.copyTo(this);
   } else if (typeof j === 'string') {
     if (j === "" || j === "0" || j === "XRP") {
       // XRP is never allowed as a Currency object

test/currency-test.js

@@ -0,0 +1,55 @@
+var assert   = require('assert');
+var utils    = require('./testutils');
+var currency = utils.load_module('currency').Currency;
+
+describe('Currency', function() {
+  describe('json_rewrite', function() {
+    it('json_rewrite("USD") == "USD"', function() {
+      assert.strictEqual('USD', currency.json_rewrite('USD'));
+    });
+    it('json_rewrite("NaN") == "XRP"', function() {
+      assert.strictEqual('XRP', currency.json_rewrite(NaN));
+    });
+  });
+  describe('from_json', function() {
+    it('from_json(NaN).to_json() == "XRP"', function() {
+      var r = currency.from_json(NaN);
+      assert(!r.is_valid());
+      assert.strictEqual('XRP', r.to_json());
+    });
+    it('from_json("XRP").to_json() == "XRP"', function() {
+      var r = currency.from_json('XRP');
+      assert.strictEqual(0, r._value);
+      assert(r.is_valid());
+      assert.strictEqual('XRP', r.to_json());
+    });
+  });
+  describe('parse_json(currency obj)', function() {
+    assert.strictEqual('USD', new currency().parse_json(currency.from_json('USD')).to_json());
+  });
+  describe('is_valid', function() {
+    it('Currency.is_valid("XRP")', function() {
+      assert(currency.is_valid('XRP'));
+    });
+    it('!Currency.is_valid(NaN)', function() {
+      assert(!currency.is_valid(NaN));
+    });
+    it('from_json("XRP").is_valid()', function() {
+      assert(currency.from_json('XRP').is_valid());
+    });
+    it('!from_json(NaN).is_valid()', function() {
+      assert(!currency.from_json(NaN).is_valid());
+    });
+  });
+  describe('clone', function() {
+    it('should clone currency object', function() {
+      var c = currency.from_json('XRP');
+      assert.strictEqual('XRP', c.clone().to_json());
+    });
+  });
+  describe('to_human', function() {
+    it('should generate human string', function() {
+      assert.strictEqual('XRP', currency.from_json('XRP').to_human());
+    });
+  });
+});