Import JUnit reports

I’m integrating a legacy build into Gradle. The project has CppUnit tests. We already have a XSLT that turns it report into a JUnit report. Since that’s a very common Java test library, I was assuming I could feed it to a org.gradle.api.tasks.testing.TestReport task, but it seems to only accept a (proprietary?!?) binary format.

Can you give me any clue how I can import JUnit reports (to effectively include CppUnit tests into the build)/