StringTest.java

import org.junit.Test;

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

public class StringTest {

    @Test
    public void should_format_string() {
        String formattedString = String.format("%s, %s, %s.", "a", "b", "c");
        assertThat(formattedString, is("a, b, c."));
    }
}

See http://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html