running `gradle test` on Debian/stretch causes 3 tests to fail

I'm in the process of updating the CI infrastructure to Debian/stretch to serve as a staging test for updating f-droid.org infrastructure to Debian/stretch. The fdroidserver image builds and tests fine. The fdroidclient builds fine, but then 3 of the tests in gradle test fail (https://clbin.com/pl2oj):

org.fdroid.fdroid.RepoUpdater$SigningException: Repository was not signed correctly: No signature found in index
	at org.fdroid.fdroid.RepoUpdater.getSigningCertFromJar(RepoUpdater.java:382)
	at org.fdroid.fdroid.RepoUpdater.processDownloadedFile(RepoUpdater.java:258)
	at org.fdroid.fdroid.updater.MultiRepoUpdaterTest.updateRepo(MultiRepoUpdaterTest.java:203)
	at org.fdroid.fdroid.updater.Issue763MultiRepo.updateMicroG(Issue763MultiRepo.java:66)
	at org.fdroid.fdroid.updater.Issue763MultiRepo.antoxAndMicroG(Issue763MultiRepo.java:76)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)

@pserwylo any ideas why? I'm mystified.

@eighthave, @cde: Out of curiosity, these are the three failing tests in fdroidclient that seem to pass when run via CI, but fail in Android Studio. I have no idea what is going on with it, as they used to pass just fine, and the files for which it reports they have no signature definitely have signatures.

Yeah, I have the same result. Its a bit mystifying. It might be because the CI builds are running on Debian/jessie, and we are running on newer releases. Running gitlab-ci with Debian/stretch will test that theory.