private void assertForceSinglePassIs(boolean expected, GroupingOperation operation) {
        assertEquals(expected, operation.getForceSinglePass(), "Force single pass is " + expected + " in " + operation);
        for (GroupingOperation child : operation.getChildren())
            assertForceSinglePassIs(expected, child);
    }
Tests the Fast searcher

@author bratseth
container-search/src/test/java/com/yahoo/prelude/fastsearch/IndexedBackendTestCase.java