This is a temporary fix to have a clear view of what is working or not
and to prevent breaking even more tests. Incomplete tests will be fixed
in the comming days/weeks.
All code for unit tests is now under the `PhpSpreadsheet\Tests` namespace
which is autoloaded via composer mechanism. So there is no need for
`require()` anymore.
Also, tests were moved in `tests/` folder and phpunit should be executed from
the project root folder. This is to conform to the de facto standard, notably
in use in phpunit itself.
Adrien Crivelli