TestGeoDataWriter has a unit test method saveAndCompare (along with saveAndCompare_data) which iterates over all .kml files in tests/data and does the following:
- parse the file, retrieve the GeoDataDocument as result
- write the document to a KML file in memory (QBuffer/QByteArray)
- compare the XML contents of the original file and the file in memory for equality.

This is fine for simple cases, but limits the possible input .kml files: They cannot have tags with default values and the order of tags must be exactly the one which Marble uses internally. To allow adding .kml files in the future as test cases which are not limited by this, write a similar unit test which does the comparison using GeoDataDocument::operator== instead of the XML string comparison. Use the existing saveAndCompare unit test as a base for a new unit test saveAndCompareEquality(). Instead of doing the QTextStream based comparison, parse the QBuffer contents, retrieve the GeoDataDocument from the parser and compare it with the original one (make sure not to compare pointers).

Make sure to compile Marble with the BUILD_MARBLE_TESTS=TRUE option enabled and run the test case from the build folder (run tests/TestEquality). Submit a review request at https://git.reviewboard.kde.org.

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