Add Money and Money Series (#505)

* Add Money class

* Standardize creation of money series

* Formatting

* Fix test

test/models/money_test.rb

@@ -0,0 +1,45 @@
+require "test_helper"
+
+class MoneyTest < ActiveSupport::TestCase
+    test "#symbol returns the currency symbol for a given currency code" do
+        assert_equal "$", Money.from_amount(0, "USD").symbol
+        assert_equal "€", Money.from_amount(0, "EUR").symbol
+    end
+
+    test "#separator returns the currency separator for a given currency code" do
+        assert_equal ".", Money.from_amount(0, "USD").separator
+        assert_equal ",", Money.from_amount(0, "EUR").separator
+    end
+
+    test "#precision returns the currency's precision for a given currency code" do
+        assert_equal 2, Money.from_amount(0, "USD").precision
+        assert_equal 0, Money.from_amount(123.45, "KRW").precision
+    end
+
+    test "#cents returns the cents part with 2 precisions by default" do
+        assert_equal "45", Money.from_amount(123.45, "USD").cents
+    end
+
+    test "#cents returns empty when precision is 0" do
+        assert_equal "", Money.from_amount(123.45, "USD").cents(precision: 0)
+    end
+
+    test "#cents returns the cents part of the string with given precision" do
+        amount = Money.from_amount(123.4862, "USD")
+        assert_equal "4", amount.cents(precision: 1)
+        assert_equal "486", amount.cents(precision: 3)
+    end
+
+    test "#cents pads the cents part with zeros up to the specified precision" do
+        amount_without_decimal = Money.from_amount(123, "USD")
+        amount_with_decimal = Money.from_amount(123.4, "USD")
+
+        assert_equal "00", amount_without_decimal.cents
+        assert_equal "40", amount_with_decimal.cents
+    end
+
+    test "works with BigDecimal" do
+        amount = Money.from_amount(BigDecimal("123.45"), "USD")
+        assert_equal "45", amount.cents
+    end
+end