diff --git a/erpnext/accounts/doctype/dunning/test_dunning.py b/erpnext/accounts/doctype/dunning/test_dunning.py
index 0110877ce90..4508738a471 100644
--- a/erpnext/accounts/doctype/dunning/test_dunning.py
+++ b/erpnext/accounts/doctype/dunning/test_dunning.py
@@ -12,6 +12,7 @@ from erpnext.accounts.doctype.sales_invoice.mapper import (
 	create_dunning as create_dunning_from_sales_invoice,
 )
 from erpnext.accounts.doctype.sales_invoice.test_sales_invoice import (
+	create_sales_invoice,
 	create_sales_invoice_against_cost_center,
 )
 from erpnext.tests.utils import ERPNextTestSuite
@@ -152,6 +153,37 @@ class TestDunning(ERPNextTestSuite):
 		dunning.reload()
 		self.assertEqual(dunning.status, "Unresolved")
 
+	@ERPNextTestSuite.change_settings(
+		"Accounts Settings", {"allow_multi_currency_invoices_against_single_party_account": 1}
+	)
+	def test_dunning_outstanding_uses_transaction_currency(self):
+		"""
+		Regression for #56006: dunning outstanding must be in the invoice transaction
+		currency, not in the party account currency.
+
+		A USD invoice posted against an INR receivable account stores
+		outstanding_amount in INR (party account currency).  The overdue payment
+		row on the resulting Dunning must carry the USD amount, not the INR amount.
+		"""
+		si = create_sales_invoice(
+			posting_date=add_days(today(), -10),
+			currency="USD",
+			conversion_rate=50,
+			rate=100,
+			debit_to="Debtors - _TC",
+		)
+
+		# Sanity-check the invoice state before creating the dunning
+		self.assertEqual(si.currency, "USD")
+		self.assertEqual(si.outstanding_amount, 5000.0)  # INR (party account currency)
+		self.assertEqual(si.payment_schedule[0].outstanding, 100.0)  # USD (transaction currency)
+
+		dunning = create_dunning_from_sales_invoice(si.name)
+
+		self.assertEqual(len(dunning.overdue_payments), 1)
+		# Must reflect 100 USD, not 5000 INR mislabelled as USD
+		self.assertEqual(dunning.overdue_payments[0].outstanding, 100.0)
+
 	def test_dunning_not_affected_by_standalone_credit_note(self):
 		"""
 		Test that dunning is NOT resolved when a credit note has update_outstanding_for_self checked.
diff --git a/erpnext/accounts/doctype/pos_invoice/test_pos_invoice_reset_mop.py b/erpnext/accounts/doctype/pos_invoice/test_pos_invoice_reset_mop.py
new file mode 100644
index 00000000000..0f0f6052576
--- /dev/null
+++ b/erpnext/accounts/doctype/pos_invoice/test_pos_invoice_reset_mop.py
@@ -0,0 +1,34 @@
+# Copyright (c) 2024, Frappe Technologies Pvt. Ltd. and Contributors
+# See license.txt
+
+# Regression test for https://github.com/frappe/erpnext/issues/56501
+# AttributeError: 'POSInvoice' object has no attribute 'is_created_using_pos'
+# when calling reset_mode_of_payments on a draft POS Invoice.
+
+from erpnext.accounts.doctype.pos_invoice.test_pos_invoice import (
+	POSInvoiceTestMixin,
+	create_pos_invoice,
+)
+from erpnext.accounts.doctype.pos_opening_entry.test_pos_opening_entry import create_opening_entry
+
+
+class TestPOSInvoiceResetModeOfPayments(POSInvoiceTestMixin):
+	def setUp(self):
+		super().setUp()
+		create_opening_entry(self.pos_profile, self.test_user.name)
+
+	def test_reset_mode_of_payments_does_not_raise_attribute_error(self):
+		"""Calling reset_mode_of_payments on a draft POS Invoice must not raise
+		AttributeError for the missing is_created_using_pos attribute.
+
+		update_multi_mode_option accesses doc.is_created_using_pos, which is a
+		field on SalesInvoice but does not exist on POSInvoice, causing the error
+		reported in #56501 when a user tries to edit a saved draft order.
+		"""
+		inv = create_pos_invoice(do_not_submit=True)
+
+		# This call must not raise AttributeError on the missing field.
+		inv.reset_mode_of_payments()
+
+		# Payments should have been repopulated from the POS profile.
+		self.assertTrue(len(inv.payments) > 0, "Payments should be populated after reset")
diff --git a/erpnext/accounts/doctype/repost_payment_ledger/test_repost_payment_ledger.py b/erpnext/accounts/doctype/repost_payment_ledger/test_repost_payment_ledger.py
index 8c2b8946121..c0498adb8a4 100644
--- a/erpnext/accounts/doctype/repost_payment_ledger/test_repost_payment_ledger.py
+++ b/erpnext/accounts/doctype/repost_payment_ledger/test_repost_payment_ledger.py
@@ -1,11 +1,55 @@
-# Copyright (c) 2022, Frappe Technologies Pvt. Ltd. and Contributors
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
 # See license.txt
 
-# import frappe
-
+import frappe
 
+from erpnext.accounts.doctype.sales_invoice.test_sales_invoice import create_sales_invoice
 from erpnext.tests.utils import ERPNextTestSuite
 
+COMPANY = "_Test Company"
+
 
 class TestRepostPaymentLedger(ERPNextTestSuite):
-	pass
+	"""Repost Payment Ledger auto-selects submitted vouchers on/after a cutoff date
+	(unless rows are added manually) and queues them for a ledger rebuild."""
+
+	def setUp(self):
+		frappe.set_user("Administrator")
+
+	def make_repost(self, **args):
+		args = frappe._dict(args)
+		doc = frappe.new_doc("Repost Payment Ledger")
+		doc.company = COMPANY
+		doc.posting_date = args.get("posting_date", "2026-06-01")
+		doc.voucher_type = args.get("voucher_type", "Sales Invoice")
+		doc.add_manually = args.get("add_manually", 0)
+		return doc
+
+	def test_loads_submitted_vouchers_on_or_after_cutoff(self):
+		after_cutoff = create_sales_invoice(company=COMPANY, posting_date="2026-06-15", rate=100, qty=1)
+		on_cutoff = create_sales_invoice(company=COMPANY, posting_date="2026-06-01", rate=100, qty=1)
+		before_cutoff = create_sales_invoice(company=COMPANY, posting_date="2026-01-15", rate=100, qty=1)
+
+		doc = self.make_repost(posting_date="2026-06-01", voucher_type="Sales Invoice")
+		doc.save()  # before_validate loads the vouchers and sets status
+
+		loaded = {v.voucher_no for v in doc.repost_vouchers}
+		self.assertIn(after_cutoff.name, loaded)
+		# the filter is >= so an invoice posted exactly on the cutoff is included
+		self.assertIn(on_cutoff.name, loaded)
+		self.assertNotIn(before_cutoff.name, loaded)
+		self.assertEqual(doc.repost_status, "Queued")
+
+	def test_add_manually_preserves_user_rows(self):
+		# manually add a BEFORE-cutoff invoice (which the filter would never load) while a
+		# matching after-cutoff invoice also exists. If auto-loading wrongly ran it would
+		# drop the manual row and pull the after-cutoff one, so this distinguishes the modes.
+		manual_si = create_sales_invoice(company=COMPANY, posting_date="2026-01-15", rate=100, qty=1)
+		create_sales_invoice(company=COMPANY, posting_date="2026-06-15", rate=100, qty=1)
+
+		doc = self.make_repost(add_manually=1, posting_date="2026-06-01")
+		doc.append("repost_vouchers", {"voucher_type": "Sales Invoice", "voucher_no": manual_si.name})
+		doc.save()
+
+		rows = [(v.voucher_type, v.voucher_no) for v in doc.repost_vouchers]
+		self.assertEqual(rows, [("Sales Invoice", manual_si.name)])
diff --git a/erpnext/accounts/doctype/sales_invoice/mapper.py b/erpnext/accounts/doctype/sales_invoice/mapper.py
index 8a8d07dea1d..46ce4753a85 100644
--- a/erpnext/accounts/doctype/sales_invoice/mapper.py
+++ b/erpnext/accounts/doctype/sales_invoice/mapper.py
@@ -594,7 +594,15 @@ def create_dunning(
 		if source.payment_schedule and len(source.payment_schedule) == 1:
 			for row in target.overdue_payments:
 				if row.payment_schedule == source.payment_schedule[0].name:
-					row.outstanding = source.get("outstanding_amount")
+					# outstanding_amount is in the party account currency, but the Overdue Payment
+					# row is in the invoice's transaction currency. When they differ, use the
+					# payment schedule's own outstanding — it is kept in transaction currency and
+					# updated as payments are allocated, so it stays correct even when the invoice
+					# and its payments post at different exchange rates (#56006).
+					if source.party_account_currency and source.party_account_currency != source.currency:
+						row.outstanding = source.payment_schedule[0].outstanding
+					else:
+						row.outstanding = source.get("outstanding_amount")
 
 		target.validate()
 
diff --git a/erpnext/accounts/doctype/sales_invoice/services/pos.py b/erpnext/accounts/doctype/sales_invoice/services/pos.py
index 9c7a7c2654c..76fc770de47 100644
--- a/erpnext/accounts/doctype/sales_invoice/services/pos.py
+++ b/erpnext/accounts/doctype/sales_invoice/services/pos.py
@@ -344,7 +344,9 @@ def update_multi_mode_option(doc, pos_profile) -> None:
 		payment.account = payment_mode.default_account
 		payment.type = payment_mode.type
 
-	mop_refetched = bool(doc.payments) and not doc.is_created_using_pos
+	# is_created_using_pos exists on Sales Invoice but not POS Invoice; use get() so this
+	# shared helper doesn't raise AttributeError when called on a POS Invoice
+	mop_refetched = bool(doc.payments) and not doc.get("is_created_using_pos")
 
 	doc.set("payments", [])
 	invalid_modes = []
diff --git a/erpnext/crm/doctype/campaign/campaign.py b/erpnext/crm/doctype/campaign/campaign.py
index f9834d2ccef..4953be544a5 100644
--- a/erpnext/crm/doctype/campaign/campaign.py
+++ b/erpnext/crm/doctype/campaign/campaign.py
@@ -26,25 +26,35 @@ class Campaign(Document):
 	# end: auto-generated types
 
 	def after_insert(self):
-		try:
-			mc = frappe.get_doc("UTM Campaign", self.campaign_name)
-		except frappe.DoesNotExistError:
-			mc = frappe.new_doc("UTM Campaign")
-			mc.name = self.campaign_name
-		mc.campaign_description = self.description
-		mc.crm_campaign = self.campaign_name
-		mc.save(ignore_permissions=True)
+		self.sync_utm_campaign()
 
 	def on_change(self):
-		try:
-			mc = frappe.get_doc("UTM Campaign", self.campaign_name)
-		except frappe.DoesNotExistError:
-			mc = frappe.new_doc("UTM Campaign")
-			mc.name = self.campaign_name
+		self.sync_utm_campaign()
+
+	def sync_utm_campaign(self):
+		mc = self.get_utm_campaign_mirror()
 		mc.campaign_description = self.description
-		mc.crm_campaign = self.campaign_name
+		# link by the document name, which differs from campaign_name when a naming series is used
+		mc.crm_campaign = self.name
 		mc.save(ignore_permissions=True)
 
+	def get_utm_campaign_mirror(self):
+		# the mirror already linked to this Campaign, if any (survives campaign_name edits)
+		if owned := frappe.db.get_value("UTM Campaign", {"crm_campaign": self.name}):
+			return frappe.get_doc("UTM Campaign", owned)
+
+		# reuse a same-named mirror only when it isn't already owned by another Campaign,
+		# otherwise two Campaigns sharing a display name would hijack each other's mirror
+		if frappe.db.exists("UTM Campaign", self.campaign_name):
+			same_name = frappe.get_doc("UTM Campaign", self.campaign_name)
+			if not same_name.crm_campaign or same_name.crm_campaign == self.name:
+				return same_name
+
+		# create a fresh mirror, keeping its name unique when the display name is taken
+		mc = frappe.new_doc("UTM Campaign")
+		mc.name = self.name if frappe.db.exists("UTM Campaign", self.campaign_name) else self.campaign_name
+		return mc
+
 	def autoname(self):
 		if frappe.defaults.get_global_default("campaign_naming_by") != "Naming Series":
 			self.name = self.campaign_name
diff --git a/erpnext/crm/doctype/campaign/test_campaign.py b/erpnext/crm/doctype/campaign/test_campaign.py
index 8876e640475..e3f41e9958f 100644
--- a/erpnext/crm/doctype/campaign/test_campaign.py
+++ b/erpnext/crm/doctype/campaign/test_campaign.py
@@ -1,9 +1,70 @@
-# Copyright (c) 2021, Frappe Technologies Pvt. Ltd. and Contributors
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
 # See license.txt
-# import frappe
+
+import frappe
 
 from erpnext.tests.utils import ERPNextTestSuite
 
 
 class TestCampaign(ERPNextTestSuite):
-	pass
+	"""Campaign names itself from the campaign name (or a naming series) and mirrors
+	itself into a UTM Campaign."""
+
+	def setUp(self):
+		frappe.set_user("Administrator")
+
+	def make_campaign(self, **fields):
+		doc = frappe.new_doc("Campaign")
+		doc.campaign_name = fields.pop("campaign_name", f"_Test Campaign {frappe.generate_hash(length=6)}")
+		doc.update(fields)
+		return doc.insert()
+
+	def test_autoname_uses_the_campaign_name_by_default(self):
+		campaign = self.make_campaign(campaign_name="_Test Campaign Named")
+		self.assertEqual(campaign.name, "_Test Campaign Named")
+
+	def test_autoname_uses_naming_series_when_configured(self):
+		# regression: with a naming series the document name differs from campaign_name,
+		# and the UTM sync must still link back to a valid Campaign (self.name)
+		original = frappe.defaults.get_global_default("campaign_naming_by")
+		frappe.defaults.set_global_default("campaign_naming_by", "Naming Series")
+		try:
+			campaign = self.make_campaign(naming_series="SAL-CAM-.YYYY.-")
+			self.assertTrue(campaign.name.startswith("SAL-CAM-"))
+			utm = frappe.get_doc("UTM Campaign", campaign.campaign_name)
+			self.assertEqual(utm.crm_campaign, campaign.name)
+		finally:
+			frappe.defaults.set_global_default("campaign_naming_by", original or "")
+
+	def test_inserting_mirrors_into_a_utm_campaign(self):
+		campaign = self.make_campaign(campaign_name="_Test Campaign UTM", description="Spring push")
+		self.assertTrue(frappe.db.exists("UTM Campaign", campaign.campaign_name))
+		utm = frappe.get_doc("UTM Campaign", campaign.campaign_name)
+		self.assertEqual(utm.campaign_description, "Spring push")
+		self.assertEqual(utm.crm_campaign, campaign.name)
+
+	def test_editing_campaign_name_reuses_the_same_utm_campaign(self):
+		campaign = self.make_campaign(campaign_name="_Test Campaign Rename A")
+		campaign.campaign_name = "_Test Campaign Rename B"
+		campaign.save()
+		# the edit updates the existing mirror rather than creating a second one
+		mirrors = frappe.get_all("UTM Campaign", filters={"crm_campaign": campaign.name})
+		self.assertEqual(len(mirrors), 1)
+
+	def test_two_campaigns_sharing_a_name_do_not_hijack_each_others_mirror(self):
+		# a naming series lets two Campaigns share a display name; each must keep its own mirror
+		original = frappe.defaults.get_global_default("campaign_naming_by")
+		frappe.defaults.set_global_default("campaign_naming_by", "Naming Series")
+		try:
+			first = self.make_campaign(campaign_name="_Test Shared Mirror", naming_series="SAL-CAM-.YYYY.-")
+			second = self.make_campaign(campaign_name="_Test Shared Mirror", naming_series="SAL-CAM-.YYYY.-")
+		finally:
+			frappe.defaults.set_global_default("campaign_naming_by", original or "")
+
+		# the first Campaign's mirror is untouched; the second gets a distinct one
+		self.assertEqual(
+			frappe.db.get_value("UTM Campaign", "_Test Shared Mirror", "crm_campaign"), first.name
+		)
+		second_mirror = frappe.db.get_value("UTM Campaign", {"crm_campaign": second.name})
+		self.assertTrue(second_mirror)
+		self.assertNotEqual(second_mirror, "_Test Shared Mirror")
diff --git a/erpnext/crm/doctype/contract_template/test_contract_template.py b/erpnext/crm/doctype/contract_template/test_contract_template.py
index 6362da2afb7..c690239856c 100644
--- a/erpnext/crm/doctype/contract_template/test_contract_template.py
+++ b/erpnext/crm/doctype/contract_template/test_contract_template.py
@@ -1,8 +1,43 @@
-# Copyright (c) 2018, Frappe Technologies Pvt. Ltd. and Contributors
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
 # See license.txt
 
+import frappe
+
+from erpnext.crm.doctype.contract_template.contract_template import get_contract_template
 from erpnext.tests.utils import ERPNextTestSuite
 
 
 class TestContractTemplate(ERPNextTestSuite):
-	pass
+	"""Contract Template validates its Jinja terms and renders them against a doc."""
+
+	def test_malformed_contract_terms_are_rejected(self):
+		doc = frappe.new_doc("Contract Template")
+		doc.contract_terms = "{% for x in %}"  # invalid Jinja
+		self.assertRaises(frappe.ValidationError, doc.validate)
+
+		# a valid template, and no template at all, both pass
+		doc.contract_terms = "Party: {{ party_name }}"
+		doc.validate()
+		doc.contract_terms = None
+		doc.validate()
+
+	def test_get_contract_template_renders_terms(self):
+		template = frappe.get_doc(
+			{
+				"doctype": "Contract Template",
+				"title": "_Test Contract Template",
+				"contract_terms": "Party: {{ party_name }}",
+			}
+		).insert()
+
+		result = get_contract_template(template.name, {"party_name": "Acme"})
+		self.assertEqual(result["contract_terms"], "Party: Acme")
+		self.assertEqual(result["contract_template"].name, template.name)
+
+	def test_get_contract_template_without_terms_returns_none(self):
+		template = frappe.get_doc(
+			{"doctype": "Contract Template", "title": "_Test Empty Contract Template"}
+		).insert()
+
+		result = get_contract_template(template.name, {})
+		self.assertIsNone(result["contract_terms"])
diff --git a/erpnext/crm/doctype/crm_settings/test_crm_settings.py b/erpnext/crm/doctype/crm_settings/test_crm_settings.py
index 64a5addefcb..e89ed263140 100644
--- a/erpnext/crm/doctype/crm_settings/test_crm_settings.py
+++ b/erpnext/crm/doctype/crm_settings/test_crm_settings.py
@@ -1,9 +1,39 @@
-# Copyright (c) 2021, Frappe Technologies Pvt. Ltd. and Contributors
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
 # See license.txt
-# import frappe
+
+import frappe
 
 from erpnext.tests.utils import ERPNextTestSuite
 
 
 class TestCRMSettings(ERPNextTestSuite):
-	pass
+	"""CRM Settings guards its Frappe-CRM sync and Contact-Us opportunity toggles."""
+
+	def make_settings(self, **fields):
+		doc = frappe.new_doc("CRM Settings")
+		doc.update(fields)
+		return doc
+
+	def test_data_sync_requires_at_least_one_allowed_user(self):
+		doc = self.make_settings(enable_frappe_crm_data_synchronization=1)
+		self.assertRaises(frappe.ValidationError, doc.validate_allowed_users)
+		# adding a user satisfies the check
+		doc.append("allowed_users", {"user": "Administrator"})
+		doc.validate_allowed_users()
+
+	def test_disabling_sync_clears_allowed_users(self):
+		doc = self.make_settings(enable_frappe_crm_data_synchronization=0)
+		doc.append("allowed_users", {"user": "Administrator"})
+		doc.clear_allowed_users()
+		self.assertEqual(doc.allowed_users, [])
+
+		# while sync is on, the rows are kept
+		enabled = self.make_settings(enable_frappe_crm_data_synchronization=1)
+		enabled.append("allowed_users", {"user": "Administrator"})
+		enabled.clear_allowed_users()
+		self.assertEqual(len(enabled.allowed_users), 1)
+
+	@ERPNextTestSuite.change_settings("Contact Us Settings", {"is_disabled": 1})
+	def test_opportunity_from_contact_us_needs_the_form_enabled(self):
+		doc = self.make_settings(enable_opportunity_creation_from_contact_us=1)
+		self.assertRaises(frappe.ValidationError, doc.validate_enable_opportunity_creation_from_contact_us)
diff --git a/erpnext/manufacturing/doctype/job_card/test_job_card.py b/erpnext/manufacturing/doctype/job_card/test_job_card.py
index bf10aa0e3f0..efb1636e7c1 100644
--- a/erpnext/manufacturing/doctype/job_card/test_job_card.py
+++ b/erpnext/manufacturing/doctype/job_card/test_job_card.py
@@ -1703,3 +1703,76 @@ def create_semi_fg_bom(semi_fg_item, raw_item, inspection_required):
 	bom.append("items", {"item_code": raw_item, "qty": 1})
 	bom.submit()
 	return bom.name
+
+
+class TestJobCardLogic(ERPNextTestSuite):
+	"""Field-level validations and pure quantity/capacity helpers, exercised on the
+	document directly so they don't need a Work Order / BOM (the integration suite does)."""
+
+	def test_processing_a_submitted_or_cancelled_card_is_blocked(self):
+		submitted = frappe.new_doc("Job Card")
+		submitted.docstatus = 1
+		self.assertRaises(frappe.ValidationError, submitted.validate_docstatus)
+
+		cancelled = frappe.new_doc("Job Card")
+		cancelled.docstatus = 2
+		self.assertRaises(frappe.ValidationError, cancelled.validate_docstatus)
+
+	def test_complete_job_card_qty_guards(self):
+		jc = frappe.new_doc("Job Card")
+		jc.for_quantity = 5
+		jc.validate_complete_job_card_qty(frappe._dict(pending_qty=3))  # within range -> passes
+		self.assertRaises(
+			frappe.ValidationError, jc.validate_complete_job_card_qty, frappe._dict(pending_qty=-1)
+		)
+		self.assertRaises(
+			frappe.ValidationError, jc.validate_complete_job_card_qty, frappe._dict(process_loss_qty=-1)
+		)
+		self.assertRaises(
+			frappe.ValidationError, jc.validate_complete_job_card_qty, frappe._dict(pending_qty=10)
+		)
+
+	def test_completed_qty_must_reconcile_with_for_quantity(self):
+		jc = frappe.new_doc("Job Card")
+		jc.for_quantity = 10
+		jc.total_completed_qty = 6
+		jc.process_loss_qty = 0
+		jc.pending_qty = 0
+		# 6 + 0 + 0 != 10 -> throws
+		self.assertRaises(frappe.ValidationError, jc.validate_completed_qty_matches_for_quantity)
+		# completed + loss + pending == for_quantity -> passes
+		jc.pending_qty = 4
+		jc.validate_completed_qty_matches_for_quantity()
+
+	def test_set_process_loss(self):
+		jc = frappe.new_doc("Job Card")
+		jc.for_quantity = 10
+		jc.total_completed_qty = 6
+		jc.pending_qty = 1
+		jc.set_process_loss()
+		self.assertEqual(jc.process_loss_qty, 3)  # 10 - 6 - 1
+
+		# no loss when nothing completed yet
+		nothing_done = frappe.new_doc("Job Card")
+		nothing_done.for_quantity = 10
+		nothing_done.total_completed_qty = 0
+		nothing_done.set_process_loss()
+		self.assertEqual(nothing_done.process_loss_qty, 0)
+
+	def test_capacity_overlap_detection(self):
+		jc = frappe.new_doc("Job Card")
+		sequential = [
+			{"from_time": "2026-01-01 10:00:00", "to_time": "2026-01-01 11:00:00"},
+			{"from_time": "2026-01-01 11:00:00", "to_time": "2026-01-01 12:00:00"},
+		]
+		overlapping = [
+			{"from_time": "2026-01-01 10:00:00", "to_time": "2026-01-01 11:00:00"},
+			{"from_time": "2026-01-01 10:30:00", "to_time": "2026-01-01 11:30:00"},
+		]
+		# sequential logs share one capacity slot; overlapping logs need two
+		self.assertEqual(len(jc.get_alloted_capacity(sequential)), 1)
+		self.assertEqual(len(jc.get_alloted_capacity(overlapping)), 2)
+		# capacity 1 overlaps with any log; capacity 2 only when both slots are taken
+		self.assertTrue(jc.has_overlap(1, sequential))
+		self.assertFalse(jc.has_overlap(2, sequential))
+		self.assertTrue(jc.has_overlap(2, overlapping))
diff --git a/erpnext/regional/doctype/import_supplier_invoice/test_import_supplier_invoice.py b/erpnext/regional/doctype/import_supplier_invoice/test_import_supplier_invoice.py
index 77143d5b9ab..a955839d1a3 100644
--- a/erpnext/regional/doctype/import_supplier_invoice/test_import_supplier_invoice.py
+++ b/erpnext/regional/doctype/import_supplier_invoice/test_import_supplier_invoice.py
@@ -1,9 +1,27 @@
-# Copyright (c) 2019, Frappe Technologies Pvt. Ltd. and Contributors
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
 # See license.txt
-# import frappe
 
+import frappe
+
+from erpnext.regional.doctype.import_supplier_invoice.import_supplier_invoice import get_country
 from erpnext.tests.utils import ERPNextTestSuite
 
 
 class TestImportSupplierInvoice(ERPNextTestSuite):
-	pass
+	"""The importer requires a default stock UOM and resolves country codes from the file."""
+
+	@ERPNextTestSuite.change_settings("Stock Settings", {"stock_uom": ""})
+	def test_validate_requires_a_default_uom(self):
+		doc = frappe.new_doc("Import Supplier Invoice")
+		self.assertRaises(frappe.ValidationError, doc.validate)
+
+	@ERPNextTestSuite.change_settings("Stock Settings", {"stock_uom": "Nos"})
+	def test_validate_passes_with_a_default_uom(self):
+		frappe.new_doc("Import Supplier Invoice").validate()
+
+	def test_get_country_resolves_a_known_code(self):
+		country = frappe.get_all("Country", filters={"code": ["!=", ""]}, fields=["name", "code"], limit=1)[0]
+		self.assertEqual(get_country(country.code), country.name)
+
+	def test_get_country_rejects_an_unknown_code(self):
+		self.assertRaises(frappe.ValidationError, get_country, "__no_such_country_code__")
diff --git a/erpnext/regional/doctype/lower_deduction_certificate/test_lower_deduction_certificate.py b/erpnext/regional/doctype/lower_deduction_certificate/test_lower_deduction_certificate.py
index 90396e4e2bf..c38636d4541 100644
--- a/erpnext/regional/doctype/lower_deduction_certificate/test_lower_deduction_certificate.py
+++ b/erpnext/regional/doctype/lower_deduction_certificate/test_lower_deduction_certificate.py
@@ -1,9 +1,48 @@
-# Copyright (c) 2020, Frappe Technologies Pvt. Ltd. and Contributors
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
 # See license.txt
-# import frappe
 
+import frappe
+from frappe.utils import add_days, getdate, today
+
+from erpnext.accounts.utils import get_fiscal_year
 from erpnext.tests.utils import ERPNextTestSuite
 
 
 class TestLowerDeductionCertificate(ERPNextTestSuite):
-	pass
+	"""The certificate validates its date range and detects overlap with an existing
+	certificate for the same supplier/category."""
+
+	def make_ldc(self, valid_from, valid_upto, fiscal_year=None):
+		doc = frappe.new_doc("Lower Deduction Certificate")
+		doc.valid_from = valid_from
+		doc.valid_upto = valid_upto
+		doc.fiscal_year = fiscal_year
+		return doc
+
+	def dup(self, valid_from, valid_upto):
+		return frappe._dict(valid_from=getdate(valid_from), valid_upto=getdate(valid_upto))
+
+	def test_are_dates_overlapping(self):
+		# existing certificate spans Mar 1 - Jun 30
+		existing = self.dup("2026-03-01", "2026-06-30")
+
+		# new period starts inside the existing one
+		self.assertTrue(self.make_ldc("2026-05-01", "2026-08-31").are_dates_overlapping(existing))
+		# new period ends inside the existing one
+		self.assertTrue(self.make_ldc("2026-01-01", "2026-04-30").are_dates_overlapping(existing))
+		# new period fully envelops the existing one
+		self.assertTrue(self.make_ldc("2026-01-01", "2026-12-31").are_dates_overlapping(existing))
+		# new period is entirely after the existing one -> no overlap
+		self.assertFalse(self.make_ldc("2026-07-01", "2026-12-31").are_dates_overlapping(existing))
+
+	def test_valid_upto_cannot_precede_valid_from(self):
+		doc = self.make_ldc(valid_from="2026-06-30", valid_upto="2026-01-01")
+		self.assertRaises(frappe.ValidationError, doc.validate_dates)
+
+	def test_dates_must_fall_within_the_fiscal_year(self):
+		fy_name, fy_start, fy_end = get_fiscal_year(today())
+		# a range inside the fiscal year is accepted
+		self.make_ldc(fy_start, fy_end, fiscal_year=fy_name).validate_dates()
+		# a valid_from before the fiscal year start is rejected
+		before_fy = self.make_ldc(add_days(fy_start, -1), fy_end, fiscal_year=fy_name)
+		self.assertRaises(frappe.ValidationError, before_fy.validate_dates)
diff --git a/erpnext/regional/italy/test_utils.py b/erpnext/regional/italy/test_utils.py
new file mode 100644
index 00000000000..f716bba8719
--- /dev/null
+++ b/erpnext/regional/italy/test_utils.py
@@ -0,0 +1,86 @@
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
+# See license.txt
+
+import types
+
+import frappe
+
+from erpnext.regional.italy.utils import (
+	append_row_as_charges,
+	get_conditions,
+	get_unamended_name,
+	update_summary_details,
+)
+from erpnext.tests.utils import ERPNextTestSuite
+
+
+class TestItalyUtils(ERPNextTestSuite):
+	"""Pure helpers behind the Italian e-invoice export."""
+
+	def test_get_conditions_builds_filter_map(self):
+		base = get_conditions({})
+		self.assertEqual(base["docstatus"], 1)
+		self.assertEqual(base["company_tax_id"], ("!=", ""))
+		self.assertNotIn("company", base)
+
+		scoped = get_conditions({"company": "_Test Company", "customer": "_Test Customer"})
+		self.assertEqual(scoped["company"], "_Test Company")
+		self.assertEqual(scoped["customer"], "_Test Customer")
+
+		# a single bound uses >=/<=, both bounds use a between range
+		self.assertEqual(get_conditions({"from_date": "2026-01-01"})["posting_date"], (">=", "2026-01-01"))
+		self.assertEqual(get_conditions({"to_date": "2026-06-30"})["posting_date"], ("<=", "2026-06-30"))
+		self.assertEqual(
+			get_conditions({"from_date": "2026-01-01", "to_date": "2026-06-30"})["posting_date"],
+			("between", ["2026-01-01", "2026-06-30"]),
+		)
+
+	def test_update_summary_details_accumulates_and_flags_exemption(self):
+		summary = {}
+		tax = frappe._dict(tax_exemption_reason="N4", tax_exemption_law="Art. 10")
+
+		update_summary_details(summary, tax, 22.0, 44.0, 200.0)
+		update_summary_details(summary, tax, 22.0, 22.0, 100.0)
+		self.assertEqual(summary["22.0"]["tax_amount"], 66.0)
+		self.assertEqual(summary["22.0"]["taxable_amount"], 300.0)
+		# exemption fields are only populated for the zero-rate bucket
+		self.assertEqual(summary["22.0"]["tax_exemption_reason"], "")
+
+		update_summary_details(summary, tax, 0.0, 0.0, 500.0)
+		self.assertEqual(summary["0.0"]["tax_exemption_reason"], "N4")
+		self.assertEqual(summary["0.0"]["tax_exemption_law"], "Art. 10")
+
+	def test_append_row_as_charges_computes_amount(self):
+		items, summary = [], {}
+		tax = frappe._dict(rate=22.0, account_head="VAT - IT", tax_exemption_reason="", tax_exemption_law="")
+		reference_row = frappe._dict(tax_amount=200.0, description="Consulting")
+
+		append_row_as_charges(items, tax, reference_row, summary)
+
+		self.assertEqual(len(items), 1)
+		row = items[0]
+		self.assertEqual(row.tax_rate, 22.0)
+		self.assertEqual(row.tax_amount, 44.0)  # 200 * 22 / 100
+		self.assertEqual(row.taxable_amount, 200.0)
+		self.assertEqual(row.item_code, "Consulting")
+		self.assertEqual(row.item_tax_rate, {"VAT - IT": 22.0})
+		self.assertEqual(summary["22.0"]["tax_amount"], 44.0)
+
+	def test_get_unamended_name(self):
+		# a doc missing the naming attributes is returned unchanged
+		plain = types.SimpleNamespace(name="ACC-SINV-2026-00001")
+		self.assertEqual(get_unamended_name(plain), "ACC-SINV-2026-00001")
+
+		# an amended doc drops the trailing amendment suffix
+		amended = frappe._dict(
+			name="ACC-SINV-2026-00001-1",
+			naming_series="ACC-SINV-.YYYY.-",
+			amended_from="ACC-SINV-2026-00001",
+		)
+		self.assertEqual(get_unamended_name(amended), "ACC-SINV-2026-00001")
+
+		# an original (non-amended) doc keeps its name
+		original = frappe._dict(
+			name="ACC-SINV-2026-00001", naming_series="ACC-SINV-.YYYY.-", amended_from=None
+		)
+		self.assertEqual(get_unamended_name(original), "ACC-SINV-2026-00001")
diff --git a/erpnext/stock/doctype/item_standard_cost/item_standard_cost.js b/erpnext/stock/doctype/item_standard_cost/item_standard_cost.js
index f867de3ab67..1d7267732b0 100644
--- a/erpnext/stock/doctype/item_standard_cost/item_standard_cost.js
+++ b/erpnext/stock/doctype/item_standard_cost/item_standard_cost.js
@@ -13,4 +13,33 @@ frappe.ui.form.on("Item Standard Cost", {
 			};
 		});
 	},
+
+	refresh(frm) {
+		frm.trigger("show_backdated_block_warning");
+	},
+
+	item_code(frm) {
+		frm.trigger("show_backdated_block_warning");
+	},
+
+	effective_date(frm) {
+		frm.trigger("show_backdated_block_warning");
+	},
+
+	show_backdated_block_warning(frm) {
+		if (frm.doc.docstatus !== 0 || !frm.doc.item_code || !frm.doc.effective_date) {
+			frm.set_intro("");
+			return;
+		}
+		frm.set_intro(
+			__(
+				"On submission, stock transactions for Item {0} cannot be posted with a date before {1} — backdated entries will be blocked.",
+				[
+					frappe.utils.escape_html(frm.doc.item_code).bold(),
+					frappe.datetime.str_to_user(frm.doc.effective_date).bold(),
+				]
+			),
+			"yellow"
+		);
+	},
 });
diff --git a/erpnext/stock/doctype/item_standard_cost/item_standard_cost.py b/erpnext/stock/doctype/item_standard_cost/item_standard_cost.py
index 62fb8e02903..c1a7a35506b 100644
--- a/erpnext/stock/doctype/item_standard_cost/item_standard_cost.py
+++ b/erpnext/stock/doctype/item_standard_cost/item_standard_cost.py
@@ -33,6 +33,25 @@ class ItemStandardCost(Document):
 		self.validate_item()
 		self.validate_effective_date()
 		self.validate_rate()
+		self.warn_backdated_transactions_will_be_blocked()
+
+	def warn_backdated_transactions_will_be_blocked(self):
+		# Heads-up while creating (R2 enforces it later on every stock voucher): once this rate is
+		# effective, the item's stock transactions cannot be dated before the effective date.
+		if not self.is_new():
+			return
+		frappe.msgprint(
+			_(
+				"Once this Standard Cost is submitted, stock transactions for Item {0} in {1} cannot be posted with a date before the Effective Date {2}. Post any backdated entries before submitting."
+			).format(
+				get_link_to_form("Item", self.item_code),
+				frappe.bold(self.company),
+				frappe.bold(frappe.format(self.effective_date, "Date")),
+			),
+			title=_("Backdated Entries Will Be Blocked"),
+			indicator="orange",
+			alert=True,
+		)
 
 	def validate_item(self):
 		if not frappe.get_cached_value("Item", self.item_code, "is_stock_item"):
diff --git a/erpnext/stock/doctype/stock_closing_entry/stock_closing_entry.py b/erpnext/stock/doctype/stock_closing_entry/stock_closing_entry.py
index 00a3b0204c4..1f8450c87c4 100644
--- a/erpnext/stock/doctype/stock_closing_entry/stock_closing_entry.py
+++ b/erpnext/stock/doctype/stock_closing_entry/stock_closing_entry.py
@@ -59,11 +59,10 @@ class StockClosingEntry(Document):
 			.where(
 				(table.docstatus == 1)
 				& (table.company == self.company)
-				& (
-					(table.from_date.between(self.from_date, self.to_date))
-					| (table.to_date.between(self.from_date, self.to_date))
-					| ((self.from_date >= table.from_date) & (table.from_date >= self.to_date))
-				)
+				# two date ranges overlap when each starts on or before the other ends;
+				# this also catches one range being fully contained within the other
+				& (table.from_date <= self.to_date)
+				& (table.to_date >= self.from_date)
 			)
 		)
 
diff --git a/erpnext/stock/doctype/stock_closing_entry/test_stock_closing_entry.py b/erpnext/stock/doctype/stock_closing_entry/test_stock_closing_entry.py
index 3485e47030f..df5c22b6be5 100644
--- a/erpnext/stock/doctype/stock_closing_entry/test_stock_closing_entry.py
+++ b/erpnext/stock/doctype/stock_closing_entry/test_stock_closing_entry.py
@@ -1,6 +1,8 @@
 # Copyright (c) 2024, Frappe Technologies Pvt. Ltd. and Contributors
 # See license.txt
 
+from unittest.mock import patch
+
 import frappe
 from frappe.utils import add_days, today
 
@@ -57,3 +59,45 @@ class TestStockClosingEntry(ERPNextTestSuite):
 		).submit()
 		self.last_closing_entry = entry.name
 		return entry
+
+
+class TestStockClosingEntryDuplicate(ERPNextTestSuite):
+	"""validate_duplicate blocks a second submitted closing entry whose date range
+	overlaps an existing one for the same scope (company + warehouse/item filters)."""
+
+	def make_closing(self, from_date, to_date, **fields):
+		doc = frappe.new_doc("Stock Closing Entry")
+		doc.company = COMPANY
+		doc.from_date = from_date
+		doc.to_date = to_date
+		doc.update(fields)
+		return doc
+
+	def submit_closing(self, doc):
+		# the closing-balance build is enqueued on submit; skip it here
+		with patch("erpnext.stock.doctype.stock_closing_entry.stock_closing_entry.enqueue"):
+			doc.submit()
+		return doc
+
+	def test_overlapping_range_is_rejected(self):
+		self.submit_closing(self.make_closing("2026-01-01", "2026-03-31"))
+		overlap = self.make_closing("2026-02-01", "2026-04-30")
+		self.assertRaises(frappe.ValidationError, overlap.insert)
+
+	def test_fully_contained_range_is_rejected(self):
+		# a range entirely inside an existing entry's range is still a duplicate
+		self.submit_closing(self.make_closing("2026-01-01", "2026-12-31"))
+		contained = self.make_closing("2026-03-01", "2026-03-31")
+		self.assertRaises(frappe.ValidationError, contained.insert)
+
+	def test_enclosing_range_is_rejected(self):
+		# and so is a range that fully encloses an existing entry's range
+		self.submit_closing(self.make_closing("2026-03-01", "2026-03-31"))
+		enclosing = self.make_closing("2026-01-01", "2026-12-31")
+		self.assertRaises(frappe.ValidationError, enclosing.insert)
+
+	def test_non_overlapping_range_is_allowed(self):
+		self.submit_closing(self.make_closing("2026-01-01", "2026-03-31"))
+		later = self.make_closing("2026-04-01", "2026-06-30")
+		later.insert()  # would raise if validate_duplicate wrongly flagged it as overlapping
+		self.assertTrue(frappe.db.exists("Stock Closing Entry", later.name))