Unit tests for the format String indexer

TestFormatStringIndexer.Java

import org.junit.Test;

import static org.hamcrest.Matchers.is;
import static org.junit.Assert.assertThat;

public class TestFormatStringIndexer {

    @Test
    public void index_simpleSpecifiers_ok() {
        final String result = FormatStringIndexer.index("there are %d apples in the %s basket that cost %f", 1);
        assertThat(result, is("there are %1$d apples in the %2$s basket that cost %3$f"));
    }

    @Test
    public void index_extendedSpecifiers_ok() {
        final String result = FormatStringIndexer.index("there are %3d apples in the %s basket that cost %5.2f", 1);
        assertThat(result, is("there are %1$3d apples in the %2$s basket that cost %3$5.2f"));
    }

    @Test
    public void index_indexedSpecifiers_ok() {
        final String result = FormatStringIndexer.index("there are %3d apples in the %1$s basket that cost %5.2f", 2);
        assertThat(result, is("there are %2$3d apples in the %1$s basket that cost %3$5.2f"));
    }

    @Test
    public void index_mixedSpecifiers_ok() {
        final String result = FormatStringIndexer.index("at %T there are %-2d apples in the %1$s basket and %<$s box that cost %,5.2f", 2);
        assertThat(result, is("at %2$T there are %3$-2d apples in the %1$s basket and %<$s box that cost %4$,5.2f"));
    }
}