Plaid balance calculator test cases

app/models/plaid_account/investments/balance_calculator.rb

@@ -1,13 +1,25 @@
 # Plaid Investment balances have a ton of edge cases.  This processor is responsible
 # for deriving "brokerage cash" vs. "total value" based on Plaid's reported balances and holdings.
 class PlaidAccount::Investments::BalanceCalculator
+  NegativeCashBalanceError = Class.new(StandardError)
+  NegativeTotalValueError = Class.new(StandardError)
+
   def initialize(plaid_account, security_resolver:)
     @plaid_account = plaid_account
     @security_resolver = security_resolver
   end
 
   def balance
-    total_investment_account_value
+    total_value = total_investment_account_value
+
+    if total_value.negative?
+      Sentry.capture_exception(
+        NegativeTotalValueError.new("Total value is negative for plaid investment account"),
+        level: :warning
+      )
+    end
+
+    total_value
   end
 
   # Plaid considers "brokerage cash" and "cash equivalent holdings" to all be part of "cash balance"
@@ -16,7 +28,16 @@ class PlaidAccount::Investments::BalanceCalculator
   # For this reason, we must manually calculate the cash balance based on "total value" and "holdings value"
   # See PlaidAccount::Investments::SecurityResolver for more details.
   def cash_balance
-    calculate_investment_brokerage_cash
+    cash_balance = calculate_investment_brokerage_cash
+
+    if cash_balance.negative?
+      Sentry.capture_exception(
+        NegativeCashBalanceError.new("Cash balance is negative for plaid investment account"),
+        level: :warning
+      )
+    end
+
+    cash_balance
   end
 
   private

app/models/plaid_account/investments/security_resolver.rb

@@ -4,6 +4,7 @@ class PlaidAccount::Investments::SecurityResolver
 
   def initialize(plaid_account)
     @plaid_account = plaid_account
+    @security_cache = {}
   end
 
   # Resolves an internal Security record for a given Plaid security ID
@@ -13,15 +14,6 @@ class PlaidAccount::Investments::SecurityResolver
 
     plaid_security = get_plaid_security(plaid_security_id)
 
-    unless plaid_security
-      report_unresolvable_security(plaid_security_id)
-      return Response.new(security: nil, cash_equivalent?: false)
-    end
-
-    if brokerage_cash?(plaid_security)
-      return Response.new(security: nil, cash_equivalent?: true)
-    end
-
     if plaid_security.nil?
       report_unresolvable_security(plaid_security_id)
       response = Response.new(security: nil, cash_equivalent?: false, brokerage_cash?: false)

test/models/plaid_account/investments/balance_calculator_test.rb

@@ -0,0 +1,83 @@
+require "test_helper"
+
+class PlaidAccount::Investments::BalanceCalculatorTest < ActiveSupport::TestCase
+  setup do
+    @plaid_account = plaid_accounts(:one)
+
+    @plaid_account.update!(
+      plaid_type: "investment",
+      current_balance: 4000,
+      available_balance: 2000 # We ignore this since we have current_balance + holdings
+    )
+  end
+
+  test "calculates total balance from cash and positions" do
+    brokerage_cash_security_id = "plaid_brokerage_cash" # Plaid's brokerage cash security
+    cash_equivalent_security_id = "plaid_cash_equivalent" # Cash equivalent security (i.e. money market fund)
+    aapl_security_id = "plaid_aapl_security" # Regular stock security
+
+    test_investments = {
+      transactions: [], # Irrelevant for balance calcs, leave empty
+      holdings: [
+        # $1,000 in brokerage cash
+        {
+          security_id: brokerage_cash_security_id,
+          cost_basis: 1000,
+          institution_price: 1,
+          institution_value: 1000,
+          quantity: 1000
+        },
+        # $1,000 in money market funds
+        {
+          security_id: cash_equivalent_security_id,
+          cost_basis: 1000,
+          institution_price: 1,
+          institution_value: 1000,
+          quantity: 1000
+        },
+        # $2,000 worth of AAPL stock
+        {
+          security_id: aapl_security_id,
+          cost_basis: 2000,
+          institution_price: 200,
+          institution_value: 2000,
+          quantity: 10
+        }
+      ],
+      securities: [
+        {
+          security_id: brokerage_cash_security_id,
+          ticker_symbol: "CUR:USD",
+          is_cash_equivalent: true,
+          type: "cash"
+        },
+        {
+          security_id: cash_equivalent_security_id,
+          ticker_symbol: "VMFXX", # Vanguard Money Market Reserves
+          is_cash_equivalent: true,
+          type: "mutual fund"
+        },
+        {
+          security_id: aapl_security_id,
+          ticker_symbol: "AAPL",
+          is_cash_equivalent: false,
+          type: "equity",
+          market_identifier_code: "XNAS"
+        }
+      ]
+    }
+
+    @plaid_account.update!(raw_investments_payload: test_investments)
+
+    security_resolver = PlaidAccount::Investments::SecurityResolver.new(@plaid_account)
+    balance_calculator = PlaidAccount::Investments::BalanceCalculator.new(@plaid_account, security_resolver: security_resolver)
+
+    # We set this equal to `current_balance`
+    assert_equal 4000, balance_calculator.balance
+
+    # This is the sum of "non-brokerage-cash-holdings".  In the above test case, this means
+    # we're summing up $2,000 of AAPL + $1,000 Vanguard MM for $3,000 in holdings value.
+    # We back this $3,000 from the $4,000 total to get $1,000 in cash balance.
+    assert_equal 1000, balance_calculator.cash_balance
+  end
+end