Shared money input should respond to change in currency (#654)

* Add step method to currency

* Change amount placeholder and step, when currency select change

* Lint

* Add test with auth

* Extract request to specific service

test/controllers/currencies_controller_test.rb

@@ -0,0 +1,12 @@
+require "test_helper"
+
+class CurrenciesControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    sign_in @user = users(:family_admin)
+  end
+
+  test "should show currency" do
+    get currency_url(id: "EUR", format: :json)
+    assert_response :success
+  end
+end

test/lib/money/currency_test.rb

@@ -46,4 +46,8 @@ class Money::CurrencyTest < ActiveSupport::TestCase
         assert_equal "12", value4.cents_str(2)
         assert_equal "123", value4.cents_str(3)
     end
+
+    test "step returns the smallest value of the currency" do
+      assert_equal 0.01, @currency.step
+    end
 end