@Test
    public void testImportance() {
        assertMetrics("importance:0.75","a b c",    "a x x b x c c c",600);
        assertMetrics("importance:0.85","a b!500 c","a x x b x c c c",1000);

        // Twice as common - twice as weighty, but total weight has the extra 300 - less than the previous
        assertMetrics("importance:0.7857","a b!200%0.05 c","a x x b x c c c",700);
        // Here higher importancy exactly offsets the lowered uniqueness
        assertMetrics("importance:0.85","a b!500%0.5 c","a x x b x c c c",1000);
    }
Calculated the same way as weight
searchlib/src/test/java/com/yahoo/searchlib/ranking/features/fieldmatch/test/FieldMatchMetricsTestCase.java