Multi-currency support: Money + Currency class improvements (#553)

* Money improvements

* Replace all old money usage

test/lib/money/currency_test.rb

@@ -0,0 +1,49 @@
+require "test_helper"
+
+class Money::CurrencyTest < ActiveSupport::TestCase
+    setup do
+        @currency = Money::Currency.new(:usd)
+    end
+
+    test "has many currencies" do
+        assert_operator Money::Currency.all.count, :>, 100
+    end
+
+    test "can test equality of currencies" do
+        assert_equal Money::Currency.new(:usd), Money::Currency.new(:usd)
+        assert_not_equal Money::Currency.new(:usd), Money::Currency.new(:eur)
+    end
+
+    test "can get metadata about a currency" do
+        assert_equal "USD", @currency.iso_code
+        assert_equal "United States Dollar", @currency.name
+        assert_equal "$", @currency.symbol
+        assert_equal 1, @currency.priority
+        assert_equal "Cent", @currency.minor_unit
+        assert_equal 100, @currency.minor_unit_conversion
+        assert_equal 1, @currency.smallest_denomination
+        assert_equal ".", @currency.separator
+        assert_equal ",", @currency.delimiter
+        assert_equal "%u%n", @currency.default_format
+        assert_equal 2, @currency.default_precision
+    end
+
+    test "can extract cents string from amount" do
+        value1 = Money.new(100)
+        value2 = Money.new(100.1)
+        value3 = Money.new(100.12)
+        value4 = Money.new(100.123)
+        value5 = Money.new(200, :jpy)
+
+        assert_equal "00", value1.cents_str
+        assert_equal "10", value2.cents_str
+        assert_equal "12", value3.cents_str
+        assert_equal "12", value4.cents_str
+        assert_equal "", value5.cents_str
+
+        assert_equal "", value4.cents_str(0)
+        assert_equal "1", value4.cents_str(1)
+        assert_equal "12", value4.cents_str(2)
+        assert_equal "123", value4.cents_str(3)
+    end
+end