try {
  ... // do something that throws an Exception
  fail() // with some message to display because the exception should have been thrown
} catch ( someException ){
  ... // some assertion on the exception
}

        try {
            provider.newFileSystem(URI.create(pathUri));
            fail("filesystem created twice!");
        } catch (FileSystemAlreadyExistsException x) {
            assertTrue(x.getMessage().contains("'foo'"));
        }

assertThatCode(() -> provider.newFileSystem(URI.create(pathUri)))
                .as("filesystem created twice!")
                .isInstanceOf(FileSystemAlreadyExistsException.class)
                .hasMessageContaining("'foo'");