Since the release of 0.11.0 when I call 'Run Test' I get 'Failed to run tests' and a message window saying 'Error'.

The repo I've been working with is here: https://github.com/angelozerr/lsp4xml
And tests have been working up until the new release.

Try lsp4xml/org.eclipse.lsp4xml/src/test/java/org/eclipse/lsp4xml/services/XMLFormatterTest.java to run a test.