Account::Sync model and test fixture simplifications (#968)

* Add sync model

* Fresh fixtures for sync tests

* Sync tests overhaul

* Fix entry tests

* Complete remaining model test updates

* Update system tests

* Update demo data task

* Add system tests back to PR checks

* More simplifications, add empty family to fixtures for easier testing

test/models/account/balance/syncer_test.rb

@@ -0,0 +1,133 @@
+require "test_helper"
+
+class Account::Balance::SyncerTest < ActiveSupport::TestCase
+  include Account::EntriesTestHelper
+
+  setup do
+    @account = families(:empty).accounts.create!(name: "Test", balance: 20000, currency: "USD", accountable: Depository.new)
+  end
+
+  test "syncs account with no entries" do
+    assert_equal 0, @account.balances.count
+
+    syncer = Account::Balance::Syncer.new(@account)
+    syncer.run
+
+    assert_equal [ @account.balance ], @account.balances.chronological.map(&:balance)
+  end
+
+  test "syncs account with valuations only" do
+    create_valuation(account: @account, date: 2.days.ago.to_date, amount: 22000)
+
+    syncer = Account::Balance::Syncer.new(@account)
+    syncer.run
+
+    assert_equal [ 22000, 22000, @account.balance ], @account.balances.chronological.map(&:balance)
+  end
+
+  test "syncs account with transactions only" do
+    create_transaction(account: @account, date: 4.days.ago.to_date, amount: 100)
+    create_transaction(account: @account, date: 2.days.ago.to_date, amount: -500)
+
+    syncer = Account::Balance::Syncer.new(@account)
+    syncer.run
+
+    assert_equal [ 19600, 19500, 19500, 20000, 20000, @account.balance ], @account.balances.chronological.map(&:balance)
+  end
+
+  test "syncs account with valuations and transactions" do
+    create_valuation(account: @account, date: 5.days.ago.to_date, amount: 20000)
+    create_transaction(account: @account, date: 3.days.ago.to_date, amount: -500)
+    create_transaction(account: @account, date: 2.days.ago.to_date, amount: 100)
+    create_valuation(account: @account, date: 1.day.ago.to_date, amount: 25000)
+
+    syncer = Account::Balance::Syncer.new(@account)
+    syncer.run
+
+    assert_equal [ 20000, 20000, 20500, 20400, 25000, @account.balance ], @account.balances.chronological.map(&:balance)
+  end
+
+  test "syncs account with transactions in multiple currencies" do
+    ExchangeRate.create! date: 1.day.ago.to_date, from_currency: "EUR", to_currency: "USD", rate: 1.2
+
+    create_transaction(account: @account, date: 3.days.ago.to_date, amount: 100, currency: "USD")
+    create_transaction(account: @account, date: 2.days.ago.to_date, amount: 300, currency: "USD")
+    create_transaction(account: @account, date: 1.day.ago.to_date, amount: 500, currency: "EUR") # €500 * 1.2 = $600
+
+    syncer = Account::Balance::Syncer.new(@account)
+    syncer.run
+
+    assert_equal [ 21000, 20900, 20600, 20000, @account.balance ], @account.balances.chronological.map(&:balance)
+  end
+
+  test "converts foreign account balances to family currency" do
+    @account.update! currency: "EUR"
+
+    create_transaction(date: 1.day.ago.to_date, amount: 1000, account: @account, currency: "EUR")
+
+    create_exchange_rate(2.days.ago.to_date, from: "EUR", to: "USD", rate: 2)
+    create_exchange_rate(1.day.ago.to_date, from: "EUR", to: "USD", rate: 2)
+    create_exchange_rate(Date.current, from: "EUR", to: "USD", rate: 2)
+
+    syncer = Account::Balance::Syncer.new(@account)
+    syncer.run
+
+    usd_balances = @account.balances.where(currency: "USD").chronological.map(&:balance)
+    eur_balances = @account.balances.where(currency: "EUR").chronological.map(&:balance)
+
+    assert_equal [ 21000, 20000, @account.balance ], eur_balances # native account balances
+    assert_equal [ 42000, 40000, @account.balance * 2 ], usd_balances # converted balances at rate of 2:1
+  end
+
+  test "fails with error if exchange rate not available for any entry" do
+    create_transaction(account: @account, currency: "EUR")
+
+    syncer = Account::Balance::Syncer.new(@account)
+
+    assert_raises Money::ConversionError do
+      syncer.run
+    end
+  end
+
+  # Account is able to calculate balances in its own currency (i.e. can still show a historical graph), but
+  # doesn't have exchange rates available to convert those calculated balances to the family currency
+  test "completes with warning if exchange rates not available to convert to family currency" do
+    @account.update! currency: "EUR"
+
+    syncer = Account::Balance::Syncer.new(@account)
+    syncer.run
+
+    assert_equal 1, syncer.warnings.count
+  end
+
+  test "overwrites existing balances and purges stale balances" do
+    assert_equal 0, @account.balances.size
+
+    @account.balances.create! date: Date.current, currency: "USD", balance: 30000 # incorrect balance, will be updated
+    @account.balances.create! date: 10.years.ago.to_date, currency: "USD", balance: 35000 # Out of range balance, will be deleted
+
+    assert_equal 2, @account.balances.size
+
+    syncer = Account::Balance::Syncer.new(@account)
+    syncer.run
+
+    assert_equal [ @account.balance ], @account.balances.chronological.map(&:balance)
+  end
+
+  test "partial sync does not affect balances prior to sync start date" do
+    existing_balance = @account.balances.create! date: 2.days.ago.to_date, currency: "USD", balance: 30000
+
+    transaction = create_transaction(account: @account, date: 1.day.ago.to_date, amount: 100, currency: "USD")
+
+    syncer = Account::Balance::Syncer.new(@account, start_date: 1.day.ago.to_date)
+    syncer.run
+
+    assert_equal [ existing_balance.balance, existing_balance.balance - transaction.amount, @account.balance ], @account.balances.chronological.map(&:balance)
+  end
+
+  private
+
+    def create_exchange_rate(date, from:, to:, rate:)
+      ExchangeRate.create! date: date, from_currency: from, to_currency: to, rate: rate
+    end
+end