Clarify backend data pipeline naming concepts (importers, processors, materializers, calculators, and syncers) (#2255)

* Rename MarketDataSyncer to MarketDataImporter

* Materializers

* Importers

* More reference replacements

test/models/balance/materializer_test.rb

@@ -0,0 +1,51 @@
+require "test_helper"
+
+class Balance::MaterializerTest < ActiveSupport::TestCase
+  include EntriesTestHelper
+
+  setup do
+    @account = families(:empty).accounts.create!(
+      name: "Test",
+      balance: 20000,
+      cash_balance: 20000,
+      currency: "USD",
+      accountable: Investment.new
+    )
+  end
+
+  test "syncs balances" do
+    Holding::Materializer.any_instance.expects(:materialize_holdings).returns([]).once
+
+    @account.expects(:start_date).returns(2.days.ago.to_date)
+
+    Balance::ForwardCalculator.any_instance.expects(:calculate).returns(
+      [
+        Balance.new(date: 1.day.ago.to_date, balance: 1000, cash_balance: 1000, currency: "USD"),
+        Balance.new(date: Date.current, balance: 1000, cash_balance: 1000, currency: "USD")
+      ]
+    )
+
+    assert_difference "@account.balances.count", 2 do
+      Balance::Materializer.new(@account, strategy: :forward).materialize_balances
+    end
+  end
+
+  test "purges stale balances and holdings" do
+    # Balance before start date is stale
+    @account.expects(:start_date).returns(2.days.ago.to_date).twice
+    stale_balance = Balance.new(date: 3.days.ago.to_date, balance: 10000, cash_balance: 10000, currency: "USD")
+
+    Balance::ForwardCalculator.any_instance.expects(:calculate).returns(
+      [
+        stale_balance,
+        Balance.new(date: 2.days.ago.to_date, balance: 10000, cash_balance: 10000, currency: "USD"),
+        Balance.new(date: 1.day.ago.to_date, balance: 1000, cash_balance: 1000, currency: "USD"),
+        Balance.new(date: Date.current, balance: 1000, cash_balance: 1000, currency: "USD")
+      ]
+    )
+
+    assert_difference "@account.balances.count", 3 do
+      Balance::Materializer.new(@account, strategy: :forward).materialize_balances
+    end
+  end
+end