The test is valid, however there are two issues with it:
1) The test scenario is exactly the same as in `testRemoveAccents()`. Thus:
  * Logic is duplicated. It is small, but still it is the same logic. Duplication hardens future maintenance of the code and its tests.
  * We break testing of the `removeAccents()` method into multiple pieces. This hardens readability and future maintenance of the test code.

It is better to create such tests as one scenario, being tested with different sets of parameters. The PHPUnit has [DataProviders](http://www.phpunit.de/manual/current/en/writing-tests-for-phpunit.html#writing-tests-for-phpunit.data-providers) feature to implement tests that way. You can check the `testAssocToXmlException()` test in the same test case for an example.

2) The tested method does not require application instance. So testing of `removeAccents()` needs to be moved from integration to unit tests. Unit tests are much faster to run, thus moving the test there will benefit for all the developers, running tests. 

Of course, I understand, that the new test was implemented just at the same place, where there had already existed test for `removeAccents()` So it is a mistake of other developer, who chose inappropriate location. But as soon as we have discovered this issue, then it is better to relocate the test.