refactor(inactive_customers): use descriptive aliases and add tests

Rename single-letter query-builder aliases (C, DT) to readable names
(customer, sales) and add report tests covering the column contract,
validation guards, and the days-since-last-order threshold.

(cherry picked from commit 8f15dd4d5d)

erpnext/selling/report/inactive_customers/inactive_customers.py

@@ -26,63 +26,63 @@ def execute(filters=None):
 	customers = get_sales_details(doctype)
 
 	data = []
-	for C in customers:
-		if cint(C[8]) >= cint(days_since_last_order):
-			C.insert(7, get_last_sales_amt(C[0], doctype))
-			data.append(C)
+	for row in customers:
+		if cint(row[8]) >= cint(days_since_last_order):
+			row.insert(7, get_last_sales_amt(row[0], doctype))
+			data.append(row)
 	return columns, data
 
 
 def get_sales_details(doctype):
-	C = frappe.qb.DocType("Customer")
-	DT = frappe.qb.DocType(doctype)
+	customer = frappe.qb.DocType("Customer")
+	sales = frappe.qb.DocType(doctype)
 
-	DateDiff = CustomFunction("DATEDIFF", ["d1", "d2"])
-	CurDate = CustomFunction("CURRENT_DATE", [])
+	date_diff = CustomFunction("DATEDIFF", ["d1", "d2"])
+	current_date = CustomFunction("CURRENT_DATE", [])
 
 	if doctype == "Sales Order":
 		total_considered = Sum(
 			Case()
-			.when(DT.status == "Stopped", DT.base_net_total * DT.per_delivered / 100)
-			.else_(DT.base_net_total)
+			.when(sales.status == "Stopped", sales.base_net_total * sales.per_delivered / 100)
+			.else_(sales.base_net_total)
 		)
-		date_col = DT.transaction_date
+		date_col = sales.transaction_date
 	else:
-		total_considered = Sum(DT.base_net_total)
-		date_col = DT.posting_date
+		total_considered = Sum(sales.base_net_total)
+		date_col = sales.posting_date
 
 	last_order_date = Max(date_col)
-	days_since_last_order = DateDiff(CurDate(), last_order_date)
+	days_since_last_order = date_diff(current_date(), last_order_date)
 
 	return (
-		frappe.qb.from_(C)
-		.inner_join(DT)
-		.on(C.name == DT.customer)
+		frappe.qb.from_(customer)
+		.inner_join(sales)
+		.on(customer.name == sales.customer)
 		.select(
-			C.name,
-			C.customer_name,
-			C.territory,
-			C.customer_group,
-			Count(DT.name).distinct().as_("num_of_order"),
-			Sum(DT.base_net_total).as_("total_order_value"),
+			customer.name,
+			customer.customer_name,
+			customer.territory,
+			customer.customer_group,
+			Count(sales.name).distinct().as_("num_of_order"),
+			Sum(sales.base_net_total).as_("total_order_value"),
 			total_considered.as_("total_order_considered"),
 			last_order_date.as_("last_order_date"),
 			days_since_last_order.as_("days_since_last_order"),
 		)
-		.where(DT.docstatus == 1)
-		.groupby(C.name)
+		.where(sales.docstatus == 1)
+		.groupby(customer.name)
 		.orderby(days_since_last_order, order=frappe.qb.desc)
 	).run(as_list=True)
 
 
 def get_last_sales_amt(customer, doctype):
-	DT = frappe.qb.DocType(doctype)
-	date_col = DT.transaction_date if doctype == "Sales Order" else DT.posting_date
+	sales = frappe.qb.DocType(doctype)
+	date_col = sales.transaction_date if doctype == "Sales Order" else sales.posting_date
 
 	res = (
-		frappe.qb.from_(DT)
-		.select(DT.base_net_total)
-		.where((DT.customer == customer) & (DT.docstatus == 1))
+		frappe.qb.from_(sales)
+		.select(sales.base_net_total)
+		.where((sales.customer == customer) & (sales.docstatus == 1))
 		.orderby(date_col, order=frappe.qb.desc)
 		.limit(1)
 	).run()

erpnext/selling/report/inactive_customers/test_inactive_customers.py

@@ -0,0 +1,59 @@
+# Copyright (c) 2024, Frappe Technologies Pvt. Ltd. and contributors
+# For license information, please see license.txt
+
+import frappe
+from frappe.utils import add_days, getdate, today
+
+from erpnext.selling.doctype.sales_order.test_sales_order import make_sales_order
+from erpnext.selling.report.inactive_customers.inactive_customers import execute
+from erpnext.tests.utils import ERPNextTestSuite
+
+
+class TestInactiveCustomers(ERPNextTestSuite):
+	def setUp(self):
+		self.customer = frappe.get_doc(doctype="Customer", customer_name="_Test Inactive Customer").insert()
+		self.last_order_date = add_days(today(), -120)
+		so = make_sales_order(
+			customer=self.customer.name,
+			transaction_date=self.last_order_date,
+			qty=5,
+			rate=200,
+		)
+		so.submit()
+		self.sales_order = so
+
+	def test_invalid_doctype_is_rejected(self):
+		self.assertRaises(
+			frappe.ValidationError,
+			execute,
+			{"doctype": "Purchase Order", "days_since_last_order": 30},
+		)
+
+	def test_non_positive_days_is_rejected(self):
+		self.assertRaises(
+			frappe.ValidationError,
+			execute,
+			{"doctype": "Sales Order", "days_since_last_order": 0},
+		)
+
+	def test_inactive_customer_is_listed_with_expected_columns(self):
+		columns, data = execute({"doctype": "Sales Order", "days_since_last_order": 30})
+
+		row = self.get_customer_row(data)
+		self.assertIsNotNone(row, "Inactive customer should be present in the report")
+
+		# Column contract: the report relies on positional access.
+		self.assertEqual(row[0], self.customer.name)
+		self.assertEqual(row[7], 1000)  # Last Order Amount inserted at index 7 (5 * 200)
+		self.assertEqual(getdate(row[8]), getdate(self.last_order_date))  # Last Order Date
+		self.assertGreaterEqual(row[9], 30)  # Days Since Last Order
+
+	def test_recent_customer_is_excluded(self):
+		_columns, data = execute({"doctype": "Sales Order", "days_since_last_order": 200})
+		self.assertIsNone(
+			self.get_customer_row(data),
+			"Customer ordering within the threshold must be excluded",
+		)
+
+	def get_customer_row(self, data):
+		return next((row for row in data if row[0] == self.customer.name), None)