test: adjust currency tests for deterministic seeded exchange rate

Seeding a current-dated USD->INR rate makes get_exchange_rate resolve
62.9 on today() instead of hitting the live API, which exposed three
tests that implicitly relied on a different/undefined current rate:

- customer: dropped its own colliding current-dated seed (ignored via
  ignore_if_duplicate, and its cleanup deleted the shared seed) and now
  asserts the quotation resolves the seeded rate via get_exchange_rate.
- exchange_rate_revaluation: the revalued rate (62.9) is now below the
  booked 80, so the revaluation is a loss (debited) rather than a gain;
  derive the gain/loss column from the sign instead of assuming a gain.
- purchase_invoice: the receipt rate was an accidental tuple (70,) that
  got discarded and recomputed to the seed; set explicit rates with the
  receipt above the invoice so the stock exchange difference is a credit,
  matching the asserted column.

erpnext/accounts/doctype/exchange_rate_revaluation/test_exchange_rate_revaluation.py

@@ -348,10 +348,15 @@ class TestExchangeRateRevaluation(ERPNextTestSuite, AccountsTestMixin):
 		je.reload()
 		self.assertEqual(je.voucher_type, "Exchange Rate Revaluation")
 		self.assertEqual(len(je.accounts), 3)
+		# A gain is credited to the gain/loss account, a loss is debited. The current
+		# exchange rate (from master data) may sit either side of the booked rate, so
+		# derive the column from the sign instead of assuming a gain.
+		gain_loss_debit = abs(total_gain_loss) if total_gain_loss < 0 else 0.0
+		gain_loss_credit = total_gain_loss if total_gain_loss > 0 else 0.0
 		expected = [
 			(usd_account, new_balance, 0.0, 100.0, 0.0),
 			(usd_account, 0.0, old_balance, 0.0, 100.0),
-			(gain_loss_account, 0.0, total_gain_loss, 0.0, total_gain_loss),
+			(gain_loss_account, gain_loss_debit, gain_loss_credit, gain_loss_debit, gain_loss_credit),
 		]
 		actual = []
 		for acc in je.accounts:

erpnext/accounts/doctype/purchase_invoice/test_purchase_invoice.py

@@ -472,7 +472,7 @@ class TestPurchaseInvoice(ERPNextTestSuite, StockTestMixin):
 		pr = frappe.new_doc("Purchase Receipt")
 		pr.currency = "USD"
 		pr.company = "_Test Company with perpetual inventory"
-		pr.conversion_rate = (70,)
+		pr.conversion_rate = 80
 		pr.supplier = "_Test Supplier USD"
 		pr.append(
 			"items",
@@ -491,7 +491,7 @@ class TestPurchaseInvoice(ERPNextTestSuite, StockTestMixin):
 
 		# Createing purchase invoice against Purchase Receipt
 		pi = create_purchase_invoice(pr.name)
-		pi.conversion_rate = 80
+		pi.conversion_rate = 70
 		pi.credit_to = "_Test Payable USD - TCP1"
 		pi.insert()
 		pi.submit()

erpnext/selling/doctype/customer/test_customer.py

@@ -17,6 +17,7 @@ from erpnext.selling.doctype.customer.mapper import (
 	make_quotation,
 	parse_full_name,
 )
+from erpnext.setup.utils import get_exchange_rate
 from erpnext.tests.utils import ERPNextTestSuite
 
 
@@ -29,20 +30,9 @@ class TestCustomer(ERPNextTestSuite):
 		frappe.defaults.set_user_default("company", company)
 		self.addCleanup(frappe.defaults.clear_user_default, "company")
 
-		# Seed a deterministic rate so the test does not depend on the live exchange-rate API.
-		rate = 83.0
-		exchange = frappe.get_doc(
-			{
-				"doctype": "Currency Exchange",
-				"date": nowdate(),
-				"from_currency": foreign_currency,
-				"to_currency": company_currency,
-				"exchange_rate": rate,
-				"for_selling": 1,
-				"for_buying": 1,
-			}
-		).insert(ignore_if_duplicate=True)
-		self.addCleanup(frappe.delete_doc, "Currency Exchange", exchange.name, force=1)
+		# Master data seeds a current-dated exchange rate, so make_quotation should
+		# resolve that rate instead of falling back to the default conversion rate of 1.0.
+		expected_rate = get_exchange_rate(foreign_currency, company_currency, nowdate())
 
 		customer = frappe.get_doc(
 			{
@@ -59,7 +49,7 @@ class TestCustomer(ERPNextTestSuite):
 		self.assertEqual(quotation.currency, foreign_currency)
 		self.assertNotEqual(flt(quotation.conversion_rate), 1.0)
 		self.assertNotEqual(flt(quotation.conversion_rate), 0.0)
-		self.assertEqual(flt(quotation.conversion_rate), rate)
+		self.assertEqual(flt(quotation.conversion_rate), flt(expected_rate))
 
 	def test_get_customer_name_dedupes_with_numeric_suffix(self):
 		# When a customer name already exists, get_customer_name appends "- <max suffix + 1>". The