Add tests utility service request

[Mungaijoe]

📌 Utility Service Request tests

This PR introduces comprehensive unit tests for the core functionality of the Utility Service Request DocType in the utility_billing app. The goal is to ensure all critical business logic functions as expected, including validation, contract generation, customer creation, and sales document generation.

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✅ What’s Covered

The following tests were added:

Test Method	Description
test_validate_contract_dates_auto_sets_end_date	Ensures end_date is auto-calculated correctly from start_date and contract_length_months.
test_on_submit_creates_customer_when_enabled	Verifies that a customer is automatically created upon submit when enabled in settings.
test_create_contract_success	Confirms a valid Contract document is created and correctly linked to the service request.
test_get_utility_bill_structure_details_returns_items	Asserts that item details are fetched from the selected utility bill structure.
test_create_sales_order_doc_creates_order_successfully	Validates successful creation of a Sales Order from a service request, with correct customer linkage.
test_create_sales_invoice_doc_creates_invoice_successfully	Validates successful creation of a Sales Invoice from a service request, with correct customer linkage.

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🧪 Test Design Considerations

• Fixtures Setup (setUp)

  • Creates test Customer, Item, and Utility Bill Structure records.
  • Tracks inserted documents in self.created_docs for cleanup.

• Clean Teardown (tearDown)

  • Deletes all documents created during tests using frappe.delete_doc.
  • Performs frappe.db.rollback() to ensure test isolation.

• Reusable Helper

  • create_utility_service_request() simplifies creation of a consistent base document with optional overrides.

• Test Isolation

  • Each test runs independently and does not rely on state from others.

• DocStrings

  • Each test contains docstrings for better understanding.

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🛠 How to Run Tests

From your Frappe bench directory:

bench --site [your-site-name] run-tests --doctype "Utility Service Request"