* Eliminate Most Scrutinizer Problems in Test Suite
Mostly minor code changes, with some annotations.
* Missed 2 php-cs-fixer Problems
They should be fixed now.
* Refinement for XIRR
Fix#2469. The algorithm used for XIRR is known not to converge in some cases, some of which are because the value is legitimately unsolvable; for others, using a different guess might help.
The algorithm uses continual guesses at a rate to hopefully converge on the solution. The code in Python package xirr (https://github.com/tarioch/xirr/) suggests a refinement when this rate falls below -1. Adopting this refinement solves the problem for the data in issue 2469 without any adverse effect on the existing tests. My thanks to @tarioch for that refinement.
The data from 2469 is, of course, added to the test cases. The user also mentions that an initial guess equal to the actual result doesn't converge either. A test is also added to confirm that that case now works.
The test cases are changed to run in the context of a spreadsheet rather than by direct calls to XIRR calculation routine. This revealed some data validation errors which are also cleaned up with this PR. This suggests that other financial tests might benefit from the same change; I will look into that.
* More Unit Tests
From https://github.com/RayDeCampo/java-xirr/blob/master/src/test/java/org/decampo/xirr/XirrTest.javahttps://github.com/tarioch/xirr/blob/master/tests/test_math.py
Note that there are some cases where the PHP tests do not converge, but the non-PHP tests do. I have confirmed in each of those cases that Excel does not converge, so the PhpSpreadsheet results are good, at least for now. The discrepancies are noted in comments in the test member.
* More Financial function extracts, this time looking at the Periodic Cashflow functions
* Initial extract of Constant Periodic Interest and Payment functions
* Extract ACCRINT() and ACCRINTM() Financial functions into their own class
Implement additional validations, with additional unit tests
Add support for the new calculation method argument for ACCRINT()
* Additional tests for Amortization functions
* Start work on breaking down some of the Financial Excel functions
* Unhappy path unit tests for Treasury Bill functions
* Codebase for Treasury Bills includes logic for a different days between settlement and maturity calculation for OpenOffice; but Open/Libre Office now uses the Excel days calculation, so this discrepancy between packages is no longer required
* We've already converted the Settlement and Maturity dates to Excel timestamps, so there's no need to try doing it again when calculating the days between Settlement and Maturity
* Add Unit Tests for the Days per Year helper function
* Extract Interest Rate functions - EFFECT() and NOMINAL() - with additional validation, and unhappy path unit tests
* First pass at extracting the Coupon Excel functions
* Simplify the validation methods
* Extended unit tests to cover all combinations of frequency and basis, including leap years
Fix for COUPDAYSNC() when basis is US 360 and settlement date is the last day of the month
* Ensure that all Financial function code uses the new Helpers class for Days Per Year
* Extract remaining Financial function unit tests into separate test classes for each function
This makes it easier to manage unit tests if they are individual files rather than all in a single file
It also provides a stepping stone toward making it easier to test Excel functions when Excel errors no longer return a string, but an actual Excel exception that can be handled more cleanly
* Additional unit tests for previously untested financial functions, and some additions to follow untested paths
* Start splitting Financial function tests out from the large FinancialTests class into individual test classes for each function