One way is to use JMockIt to deactivate the certificate check. Since JMockIt (and other Mocking Frameworks) work via instrumentation, any class can be modified. Here is an example as to how to mock the part of the ClassLoader, that causes the troubles:
@BeforeSuite
public void deactivateCertChecker() {
new MockUp<ClassLoader>() {
@Mock
void checkCerts(final String name, final CodeSource cs) {}
};
}
Mind you though, that this is not a fix for actually running a program that has signing issues, as the effect is only available during test runs, when mocking has been instrumented.