The tests stay; they just no longer run in separate processes. I think that only 2 tests still require separate processes - Helper/SampleTest and Tcpdf/NoDieTest. Aside from a new internal method in IOFactory, all the changes here are to test members.
PhpSpreadsheet treats CODE and UNICODE as equivalent, likewise for CHAR and UNICHAR. They are, in fact, different. CODE and CHAR deal only with single-byte character sets (Windows-1252 or MacRoman), while UNICODE and UNICHAR deal with all of Unicode. This PR separates them. The existing unit test for CODE was, in many cases, applicable to UNICODE (for which there was no separate test). The tests are corrected for CODE, new tests are added, and a separate test for UNICODE is added. CHAR was mostly okay, new tests are added, and a separate test for UNICHAR is added.
See [Discussion 4724](https://github.com/PHPOffice/PhpSpreadsheet/discussions/4724)
PhpSpreadsheet converts all control characters (x00-x1f) in strings to and from a form which Excel recognizes (e.g. `x1c` becomes `_x001C_` when writing, and vice versa when reading). There have historically been 3 exceptions which go unconverted - tab (x09), line feed (new line) (x0a), and carriage return (x0d). PR #4536 removed those exceptions, but that caused some problems; these were fixed by PR #4619, but the exceptions were restored.
The referenced discussion deals with a spreadsheet with a cell containing `_x000D_`, carriage return. Although the writer no longer converts to that string on output, the reader should be able to handle it on input. In fact, the reader ought to handle any string of the form "underscore x 4-hex-digits underscore", whether or not it represents a control character.
And there's an interesting edge case. If a user enters into a cell the string `A_x0030_B`, it needs to be handled as-is. Excel handles this by writing it out as `A_x005F_x0030_B`, i.e. substituting `_x005F_` for the first underscore, so that the reader sees `_x005F_` (converting it to underscore) followed by `x0030_B` (no leading underscore, so no conversion). PhpSpreadsheet could probably handle this by converting all underscores on write, but I am trying to emulate Excel and do it only when needed.
Ran into a surprising hitch when Php8.5 failed unit tests despite nightly succeeding. Duplicated problem locally, and fixed it with a Phpunit upgrade. Hopefully that will work on Github as well.
In PR #4716, @RobinvanderVliet points out that Cell::setValueExplicit and Worksheet::setCellValueExplicit are strangely inconsistent, where the latter requires you to specify a DataType but the former does not. The fix in that PR is to make the latter offer a default DataType rather than requiring the parameter. While that does eliminate inconsistency, I think it does so in the wrong direction - the solution should be to eliminate the optionality in the former - an implicit value for setValueExplicit just doesn't make sense. We can't do that without a breaking change, which this is not. However, we can update the doc-block and change log to indicate our intention to make that change in the next breaking release.